Searches for high redshift galaxies using gravitational lensing

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High-Redshift Supernovae and the Metal-Poor Halo Stars Signatures of the First Generation o

a r X i v :a s t r o -p h /9701093v 1 15 J a n 1997High Redshift Supernovae and the Metal-Poor Halo Stars:Signatures of the First Generation of GalaxiesJordi Miralda-Escud´e 1,2,3and Martin J.Rees 1,31Institute for Advanced Study,Princeton,NJ 085402University of Pennsylvania,Dept.of Physics and Astronomy,David Rittenhouse Lab.,209S.33rd St.,Philadelphia,PA 19104(present address)3Institute of Astronomy,University of Cambridge,Cambridge CB30HA,UK ReceivedABSTRACTRecent evidence on the metal content of the high-redshift Lyαforest seen in quasar spectra suggests that an early generation of galaxies enriched the intergalactic medium(IGM)at z∼>5.We calculate the number of supernovae that need to have taken place to produce the observed metallicity.The progenitor stars of the supernovae should have emitted∼20ionizing photons for each baryon in the universe,i.e.,more than enough to ionize the IGM.We calculate that the rate of these supernovae is such that about one of them should be observable at any time per square arc minute.Theirﬂuxes are,of course, extremely faint:at z=5,the peak magnitude should be K=27with a duration of∼1year.However,these supernovae should still be the brightest objects in the universe beyond some redshift,because the earliest galaxies should form before quasars and they should have very low mass,so their luminosities should be much lower than that of a supernova.We also show that,under the assumption of a standard initial mass function, a signiﬁcant fraction of the stars in the Galactic halo should have formed in the early galaxies that reionized and enriched the IGM,and which later must have merged with our Galaxy.These stars should have a more extended radial distribution than the observed halo stars.Subject headings:Galaxy:halo-galaxies:formation-large-scale structure of universe-quasars:absorption lines-supernovae:general1.IntroductionEver since the discovery of theﬁrst high-redshift quasar(Schmidt1965),quasars have maintained their title as the objects with the highest known redshift;the present record holder is a quasar at z=4.89(Schmidt,Schneider,&Gunn1991).Nevertheless,the highest known redshifts of galaxies have followed closely behind,with bright radio galaxies having been found up to z=4.45(Lacy et al.1994;Rawlings et al.1996);more recently, galaxies with high star formation rates have been identiﬁed from interstellar absorption lines at z=2to3(Steidel et al.1996)and from the Lyαemission line at z=4.55(Hu& McMahon1996).In fact,if quasars are related to supermassive black holes that formed in the centers of high-redshift galaxies,we should expect that many galaxies already existed before theﬁrst quasars appeared.In any‘bottom-up’theory where the observed structure in the universe forms by hierarchical gravitational collapse,and the primordial densityﬂuctuations extend to suﬃciently small scales,theﬁrst galaxies to form must have had much smaller masses than the present galaxies.Theﬁrst stars should have formed in systems with velocity dispersions of∼10Km s−1or lower,corresponding to the lowest temperatures(T∼104 K)that allow cooling and dissipation of the gas by atomic processes(systems with even lower virial temperatures can cool and dissipate through molecular hydrogen,but this cooling process should be suppressed by photodissociation of the molecules after emission of a number of UV photons that is much smaller than that needed to reionize the universe; see Haiman,Rees,&Loeb1996).These systems would be very unlikely to form quasars, because even a small fraction of their baryons turning into stars should provide suﬃcient energy(via ionization,stellar winds or supernovae)to expel the remaining gas from the shallow potential well(e.g.,Couchman&Rees1986;Dekel&Silk1986).Deeper potential wells,forming at later epochs,are probably needed to form supermassive black holes ingalactic centers.Even if all the baryons were converted into stars very eﬃciently in these early dwarf galaxies,with a baryonic mass M b∼<108M⊙,their total stellar luminosity would be much smaller than in L∗galaxies at present,simply due to their small mass.Since only a small fraction of the baryons in these systems is likely to turn into stars before the gas is ejected, the total stellar mass in theﬁrst galaxies to form in the universe should be much smaller than108M⊙.This implies that a supernova in one of theseﬁrst galaxies to form will be far brighter than the galaxy itself.Thus,the brightest probes of the era when the reionization of the intergalactic medium(IGM)started should be supernovae in very small galaxies, caused by the death of the same stars responsible for theﬁrst ionizing photons.In this paper,we shall estimate the number of supernovae that should have taken place in these galaxies and should be observable at very high redshift,and their apparent magnitudes.2.Rate of High Redshift SupernovaeThe scenario where theseﬁrst small galaxies caused the reionization of the universe is strongly supported by recent evidence that the metal abundance in the Lyαforest absorption lines with N HI∼>1014cm−2is typically Z∼10−2Z⊙,from observations of CIV lines(see Tytler et al.1995,Songaila&Cowie1996and references therein).There is relatively little uncertainty in the number of UV photons that were emitted by the stars that produced a given mass of heavy elements,because the heavy elements originate from the supernovae resulting from the same stars that emit most of the ionizing photons (although the C/O ratio is more uncertain because carbon is more abundantly produced in lower mass stars).According to the most recent calculations(Madau&Shull1996 and references therein),the energy of Lyman continuum photons emitted is0.2%of the rest-mass energy of the heavy elements produced.Thus,the energy emitted in ionizingphotons per baryon is0.002m p c2¯Z=2¯Z MeV,where¯Z is the average metallicity of all baryons in the universe,so only¯Z=10−5is needed to have emitted one ionizing photon for each baryon.If¯Z=10−2Z⊙=2×10−4,then20ionizing photons must have been emitted per baryon when the heavy elements were made.Furthermore,if these were the photons responsible for reionizing the universe,then each baryon must have recombined20times on average during the reionization epoch.This is a reasonable number,because a fraction of these photons were probably absorbed in the systems where the stars were born before the gas was expelled,and those that escaped could also have been absorbed in Lyman limit systems before the universe became transparent.Thus,there is no need to invoke ejection of gas by more massive galaxies that can accrete the ionized IGM to explain a metallicity ¯Z=10−2Z⊙.We can now calculate the number of supernovae that were required for enriching the gas in the IGM to the average metallicity of Z=2×10−4that is observed in the Lyαforest at z≃3.This number should depend only on the IGM density and the supernova yields,and should be independent of any other details related to the theory for galaxy formation and the type of galaxies that ejected the enriched gas.Recent simulations of cold dark matter models show that the absorption lines in the Lyαforest can be identiﬁed with the IGM,with densityﬂuctuations caused by gravitational collapse,and that most of the baryons should be in the IGM in these models(Cen et al.1994,Hernquist et al.1996, Miralda-Escud´e et al.1996).Thus,it is reasonable to assume that the high-z supernovae enriched all the baryons in the universe to a mean at metallicity at least as high as that of the Lyαforest.Since each supernova produces an average of∼1M⊙of heavy elements(with uncertainties depending on the assumed initial mass function and supernova models; see Woosley&Weaver1995),this implies that a supernova took place at high redshiftfor each5000M⊙of baryons in the universe.We shall assume a high baryon densityΩb=0.025h−2,in agreement with the primordial deuterium abundance measured by Burles&Tytler(1996)and by Tytler,Fan,&Burles(1996).Notice that this implies that most of the baryons at the present time are dark,so many more baryons than those we observe in galaxies had to be enriched at high redshift.Assuming theΩ=1 cosmological model,the total mass of baryons in a redshift shell of width∆z around us is M b=(6c3Ωb)/(GH0)[1−(1+z)−1/2]2/(1+z)3/2∆z,where H0is the present Hubble constant.With the above rate of supernovae per baryon mass(assumed to take place within the epoch corresponding to the redshift shell∆z),and taking into account that the supernovae within the shell would be seen by us over a time interval H−10∆z/(1+z)3/2,the total supernova rate observed over all the sky isR Sup=1.8×108h−2[1−(1+z)−1/2]2yr−1.(1) or,for z∼5,about1supernova per square arc minute per year.3.Apparent MagnitudesMost of these supernovae should be Type II which,if the progenitor is a red supergiant, have a plateau of the luminosity in their lightucurves from1to80days after the explosion, with L≃3×1042erg/s(Woosley&Weaver1986).A note of caution should be made here, in that the low-metallicity progenitors of these early supernovae could be very diﬀerent from the high metallicity counterparts.As illustrated by the case of SN1987A,it is probably not possible at this stage to predict the type of supernovae we should expect from thisﬁrst generation of stars;in particular,the possibility that some supernovae might reach higher intrinsic luminosities than regular Type IIs should be kept in mind.A duration of80days would be redshifted to more than a year at redshifts z>4,where the supernovae from stars responsible for the reionization of the universe should occur.At any random timethere should therefore be one or more supernovae per square arc minute visible in the sky. Of course,many more supernovae should have occurred in more massive galaxies at later epochs(producing the metals in stars and interstellar gas at present),and possibly in small systems that ejected their gas and continued to enrich the IGM.The main diﬃculty in detecting these supernovae is obviously the extremely faintﬂux expected.Supernovae should be the brightest objects in the universe at very high redshift,but they are of course much fainter than quasars and,as the redshift increases,the bolometricﬂuxes decrease at least as rapidly as(1+z)2.One should point out,however, that when observing at aﬁxed,long wavelenth such that the supernovae are observed on the Rayleigh-Jeans part of the spectrum,theﬂux actually becomes brighter as1+z,in the limit of high redshift.To estimate the apparent magnitudes of the supernovae,we assume a blackbody spectrum,which is a suﬃciently close approximation for our purpose.In Figure1we show the apparent magnitudes in several bands for a luminosity L=3×1042erg/s,and temperatures T=25000K and T=7000K.The high temperature is reached∼1day after the explosion,when the luminosity drops to the value in the plateau part of the lightcurve;during the next few days the temperature cools,reaching a value near7000K after about a week,and then it stays constant until the luminosity starts decreasing. Immediately after the explosion,when the shock reaches the surface of the star,the luminosity and temperature can be much higher and the apparentﬂux can be brighter by a factor∼10relative to the values in Fig.1,but this phase only lasts for∼1hour.The apparent magnitudes have been calculated for theΩ=1model with H0=70Km/s/Mpc, from theﬂux at the central wavelengths of the bands,using the central wavelengths and zero-magnitudeﬂuxes given in Allen(1973).The high-redshift cutoﬀin the curves in Figure 1indicate the redshift where the supernova light would be absorbed by the Lyαforest.At high redshift,the supernovae must obviously be searched in the infrared.The faintest galaxy surveys from the ground have reached magnitudes K≃25(Cowie et al.1994).From Fig.1,type II supernovae would have similar magnitudes at z≃2.5, although searching for variable objects should require more telescope time than simple object identiﬁcation.In order toﬁnd supernovae at redshifts higher than known quasars, fainterﬂuxes by a factor of5−10need to be detected.This might be achieved with implementation of adaptive optics on large ground-based telescopes;in the longer term,the New Generation Space Telescope should certainly be capable to observe these supernovae (see Mather&Stockman1996).We emphasize again the large uncertainty in predicting the types and absolute magnitude of supernovae from these early generation of stars.One possibility to detect these supernovae before more powerful telescopes and cameras in the infrared can be built is to use the magnifying power of gravitational lensing in galaxy clusters.The deﬂection angles of the most massive clusters of galaxies are as large as b∼30′′,with critical lines of total length of several arc minutes.The cross section for magnifying a source by more than a factor A is∼πb2/A2,or0.01square arc minutes for A=10.Thus,any rich lensing cluster should have a1%chance of having a high-redshift supernova magniﬁed by a factor larger than10at any time.The highly magniﬁed images would always appear in pairs around critical lines,and would be simple to identify only from their positions and colors given a lensing model of the cluster(see Miralda-Escud´e& Fort1993).Later,variability would have to be detected to distinguish the supernova from a faint,compact galaxy.4.The Present Distribution of Population III StarsWe have suggested in this paper that,under reasonable assumptions,supernovae should be the brightest objects in the universe beyond some redshift,in particular during theearly phases of the reionization.The supernovae might therefore be theﬁrst observational evidence we shall have of this epoch,when the very faint apparent magnitudes expected are observable.The other observable signature of this epoch may be the21cm absorption or emission by the neutral intergalactic gas(Scott&Rees1994;Madau,Meiksin&Rees 1996).The UV and heavy elements abundance inferred from quasar absorption lines allow us, as we have seen,to draw quantitative conclusions about the minimum number of high-mass stars formed beyond z=5:to produce a metallicity Z=2×10−4requires one supernova for each∼5000M⊙of baryons.This inference is quite robust,being insensitive to the details of structure and galaxy formation at high redshift,which of course depend on the cosmological assumptions.However,the total mass of stars formed depends on the IMF,and is therefore much more uncertain.For a standard IMF,∼100M⊙of stars need to be formed to produce one supernova,so2%of the baryons should have been turned into stars by the time the IGM reached this level of enrichment.Notice that this is equivalent to20%of the observed baryons in galaxies today,given our adopted value ofΩb which implies that only∼10%of the baryons are in known stars and gas in galaxies.It is of course quite possible that the IMF was diﬀerent for these early stars,given the diﬀerent physical environment(a higher ambient temperature,absence of heavy elements to act as coolants and provide opacity, and no signiﬁcant magneticﬁelds).Direct clues to the slope of the high-mass IMF may come from(for instance)the relative ionization levels of H and He and heavy elements, which depend on the background radiation spectrum shortward of the Lyman limit,or from relative abundances of heavy elements relative to carbon.Conceivably,all the early stars might be of high-mass,so that no coeval low-mass stars survive;at the other extreme,the early IMF could have been much steeper than the standard one,in which case there could be many pregalactic brown dwarfs.Would any of these“Population III”stars be observable today?Let us consider the observational consequences of the simplest assumption:that the early IMF was the same as in the solar neighborhood.In that case,most of the present luminosity from the Population III would arise from red giants and stars at the tip of the main-sequence,with M∼0.8M⊙. Where should these stars be today?After theﬁrst galaxies ejected all their gas back to the IGM,the stars that had been formed should have remained in orbit near the center of the dark matter halos.The stars then behave as collisionless matter as the halos merge with larger objects,until the present galaxies are formed.We would therefore expect that these stars would at present be distributed approximately like the dark matter in galactic and cluster halos,and in addition there should be some surviving galaxies from that epoch which have not merged into much larger objects(or have survived in orbit after merging with a large halo,having escaped tidal disruption)and still have the Population III stars in their centers.The halos of stars formed in this way around galaxies might be somewhat more centrally concentrated than the dark matter,if many mergers take place with only a moderate increase of the halo mass at each merger(so that dynamical friction is eﬀective after each merger and it can bring the stars near the center of the newly formed halo before tidal disruption occurs).In fact, particles that start near the centers of halos that merge tend to end up near the center of the merger product(e.g.,Spergel&Hernquist1992).The known halo stars have a very steep density proﬁle,ρ∝r−3.5,and their total mass is M∼109M⊙(e.g.,Morrison1993).This mass is comparable to the total mass we would expect in the halo in the Population III stars,if the total mass of the halo of our Galaxy is5×1011M⊙,with a baryon fraction of10%,and if2%of the baryons formed Population III stars.Therefore,if the stellar mass function in theﬁrst galaxies was normal,a sizable fraction of the halo stars should have originated there(this is not surprising,because it isderived from the assumption that the halo stars created their own metal abundance).It seems diﬃcult that the process of dynamical friction alluded to above can result in the steep slope of the halo stars.However,the halo density proﬁle might become shallower at large radius(see Hawkins1983and Norris&Hawkins1991for current observational evidence on this possibility),and a second halo population in the outer part of the galaxy(R∼100 Kpc)might be the remnant of the Population III.These halo stars could be found in the Hubble Deep Field(HDF,Williams et al.1996).If the stellar mass of this outer halo is 109M⊙,there should be∼108stars near the main-sequence turnoﬀ,i.e.,we expect a few stars in the HDF(with area4.4arcmin2);these would have colors I−V≃1.5,I∼25at distances of100Kpc.From Fig.2in Flynn,Gould,&Bahcall,we see that there is at least one stellar object with these characteristics in the HDF.Several other observations may help to test the existence of the Population III stars. An outer stellar halo would also imply a certain number of high-velocity stars near the solar neighborhood.A stellar population may be found in the halos of external galaxies,with density proﬁles similar to the dark matter.Sackett et al.(1994)found a luminous haloin the galaxy NGC5907with M/L=500(i.e.,about ten times more light than what we expect for the Population III).Planetary nebulae could also be found in nearby halos of galaxies or galaxy groups;several of them were reported recently by by Theuns&Warren 1996)in the Fornax cluster.There is also the possibility that the IMF in the early galaxies produced a large number of brown dwarfs.In this case,a large fraction of the baryons could have been turned into brown dwarfs,and these could be detected in ongoing microlensing experiments towards the LMC(see Paczy´n ski1996).If the baryon fraction in the universe is10%,the optical depth of these brown dwarfs toward the LMC could be as high as a few times10−8.Finally,we notice that the metallicity distribution of the Population III stars is diﬃcultto predict.If only a small fraction of the neutral IGM collapsed to galaxies before the reionization,then the gas in these galaxies could reached high metallicities and formed stars, and the metallicity could have diluted in the IGM when the gas was ejected.At the same time,the metal abundance of the IGM after reionization could be highly inhomogeneous, so some galaxies formed later could have very low metallicities.Therefore,it is diﬃcult to predict even if the average metal abundance of the Population III stars should be higher, lower or similar to the more centrally concentrated halo stars,let alone the distribution of these metallicities.5.ConclusionsAs the observational techniques improve our ability to detect extremely faint sources, and higher redshift objects can be searched for to continue unravelling the history of galaxy formation,supernovae should become the brightest observable sources.These supernovae created the heavy elements that were expelled to the IGM,and their progenitor stars are the most likely sources of the photons that reionized the universe.The expected rates of these supernovae,calculating under the assumption of a high baryon density(Ωb h2=0.025), and an average metal production of¯Z=10−2Z⊙,is as high as1supernova per square arc minute per year.To detect the supernovae,theﬂux limits of the faintest sources detectable with our telescopes will probably need to be pushed by another∼2magnitudes,although theﬁrst examples might be discovered at brighterﬂuxes behind clusters of galaxies,using the lensing magniﬁcation.Any low-mass stars that were formed in theﬁrst small galaxies where these supernovae took place should be observable today.We have argued that,if the IMF in these galaxies was similar to the present one in our galactic disk,the Population III stars are likely to account for a large fraction of the stars in our galactic halo,although most of them shouldbe in an as yet undetected outer halo with a shallower density proﬁle than the known,inner stellar halo.We thank Len Cowie,Andy Gould and John Norris for stimulating discussions.JM acknowledges support by the W.M.Keck Foundation at IAS.REFERENCESAllen,C.W.1973,Astrophysical Quantities(London:Athlone Press)Burles,S.,&Tytler,S.1996,submitted to Science(astroph9603069)Cen,R.,Miralda-Escud´e,J.,Ostriker,J.P.,&Rauch,M.1994,ApJ,437,L9 Couchman,H.M.P.,&Rees,M.J.,1986,MNRAS,221,53Cowie,L.L.,Gardner,J.P.,Hu,E.M.,Songaila,A.,Hodapp,K.-W.,& Wainscoat,R.J.1994,ApJ,434,114Dekel,A.,&Silk,J.1986,ApJ,303,39Flynn,C.,Gould,A.,&Bahcall,J.N.1996,ApJ,466,L55Haiman,Z.,Rees,M.J.,&Loeb,A.1996,ApJ,submitted(astroph-9608130) Hawkins,M.S.1983,MNRAS,206,433Hernquist,L.,Katz,N.,Weinberg,D.H.,&Miralda-Escud´e,J.1996,ApJ,457,L51 Hu,E.M.,&McMahon,R.G.1996,Nature,382,231Lacy,M.,et al.1994,MNRAS,271,504Madau,P.,Meiksin,A.,&Rees,M.J.1996,ApJ,submitted(astroph9608010) Madau,P.,&Shull,J.M.1996,ApJ,457,551Mather,J.,&Stockman,H.1996,NASA Report.Miralda-Escud´e,J.,&Fort,B.1993,ApJ,417,5Miralda-Escud´e,J.,Cen,R.,Ostriker,J.P.,&Rauch,M.1996,ApJ,471,582Morrison,H.L.1993,AJ,106,578Norris,J.,&Hawkins,M.S.1991,ApJ,380,104Paczy´n ski,B.1996,ARA&A,34,XXXRawlings,S.,Lacy,M.,Blundell,K.M.,Eales,S.A.,Bunker,A.J.,&Garrington,S.T.1996,Nature,383,502Sackett,P.D.,Morrison,H.L.,Harding,P.,&Boroson,T.A.1994,Nature,370,441Schmidt,M.1965,ApJ,141,1295Schneider,D.P.,Schmidt,M.,&Gunn,J.E.1991,AJ,101,2004Scott,D.,&Rees,M.J.1990,MNRAS,247,510Songaila,A.,&Cowie,L.L.1996,AJ,in press(astro-ph9605102)Spergel,D.N.,&Hernquist,L.1992,ApJ,397,L75Steidel,C.C.,Giavalisco,M.,Pettini,M.,Dickinson,M.,&Adelberger,K.L.1996,ApJ, 462,L17Theuns,T.,&Warren,S.J.1996,submitted to MNRAS(astro-ph9609076)Tytler,D.,Fan,X.-M.,Burles,S.,Cottrell,L.,Davis,C.,Kirkman,D.,&Zuo,L.1995,in QSO Absorption Lines,ed.G.Meylan,p.289Tytler,D.,Fan,X.-M.,&Burles,S.1996,Nature,381,207Williams,R.,et al.1996,Science with the Hubble Space Telescope II,eds.P.Benvenuti,F.D.Macchetto,&E.J.Schreier(Baltimore:STScI),in pressWoosley,S.E.,&Weaver,T.A.1995,ApJS,101,181Woosley,S.E.,&Weaver,T.A.1986,ARA&A,24,205Fig.1.—Apparent magnitude of a supernova as a function of redshift in diﬀerent bands,as labeled in theﬁgure,for two diﬀerent temperatures.We assume the supernova spectrum is a blackbody with the luminosity and temperature indicated.Supernovae Type II generally have a plateau of constant luminosity in their lightcurves with the value assumed in thisﬁgure lasting for80days.A temperature of25000K is reached∼two days after the explosion, and a week later the temperature has dropped to near7000K,where it stays constant for the next two months.。

thehitchhikersguidetothegalaxy银河系漫游指南

Searching for the answers to life, the universe, and everything? Well look no further…The Hitchhikers Guide to the GalaxyBy Douglas AdamsPublished by Serious Productions© 1976A Sci-fi thrillerPage Count: 216Your Guide to SurvivalBy ATPlanning on taking a quick stop by Ursa Minor? Just don’t forget the number one rule of thumb when traveling across the galaxy: Always bring a blanket. Tips like these are shared periodically throughout The Hitchhiker’s Guide to the Galaxy, by Douglas Adams. In it, the deepest questions of the universe will at last be answered. The protagonist, Arthur Dent, is the sole survivor of planet Earth since it was destroyed for the means of making an intergalactic highway. Dent finds himself aboard a spaceship with Ford Prefect, his quirky best friend. Together they make their way across the galaxy through a series of highly improbable coincidences: stumbling upon the president of the galaxy, surviving in the vacuum of space, and finding the legendary planet of Magrathea. The novel’s plot revolves around what happens to this unlikely crew as they are the first beings in five million years to reach Magrathea. This concept of life outside of Earth and traveling through great distances of space is what will likely keep the reader reading.In the beginning this world renowned book pulls readers in through Adams unique tone including multiple hilarious scenes that will leave one laughing out loud. The book is comprised of twenty-two chapters, each short in length making the book a quick and easy read. It also has many elements that many teenagers enjoy including humor while maintaining a thought-provoking plot line.The strong suit of The Hitchhiker’s Guide to the Galaxy is definitely its extensive creativity. Within the book there is another book entitled The Hitchhiker’s Guide to the Galaxy, where one will find descriptions of creatures and places throughout the galaxy. Some of its excerpts being literally out of this world! Who could have thought of its description of the Babble Fish: “it feeds on brainwave energy received not from its carrier but from those around it. It absorbs all unconscious mental frequencies from this brainwave energy to nourish itself.” These overly complex ideas put a comic spin on the plot which is another strength. However straying from the plot to explain something can often make readers confused. This drift from the plot resulted in a very disorganized composite of certain scenes in the book. Adams may have chose to include this skipping around to lighten up the more serious parts of the book and remind the reader that it is a comic novel. In other words those looking for an uplifting and humorous book about life’s greatest mysteries will surely find The Hitchhiker’s Guide to the Galaxy very entertaining. After reading this, one can not help but ponder the very insignificance that our whole planet really has.Douglas Adams’ other books exhibit his passion for science fiction, specifically the larger world that exists outside of Earth. The Hitchhiker’s Guide to the Galaxy was adapted into a mini TV series, and a full length feature film, in 2005. Adams has a series of follow up books entitled The Restaurant at the End of the Universe, Life the Universe and Everything, So Long, and Thanks for all the Fish, and many others. These novels include many jokes originating from The Hitchhikers Guide to the Galaxy. Adams’ career of wild success spun off of this one ground breaking novel, a truly remarkable feat.Unfortunately his career came to an abrupt end when he died at the age of forty-nine in2001. His legacy lives on through this, and many other captivating books that will leave one wondering whether or not we are indeed alone in the universe.Below is given annual work summary, do not need friends can download after editor deleted Welcome to visit againXXXX annual work summaryDear every leader, colleagues:Look back end of XXXX, XXXX years of work, have the joy of success in your work, have a collaboration with colleagues, working hard, also have disappointed when encountered difficulties and setbacks. Imperceptible in tense and orderly to be over a year, a year, under the loving care and guidance of the leadership of the company, under the support and help of colleagues, through their own efforts, various aspects have made certain progress, better to complete the job. For better work, sum up experience and lessons, will now work a brief summary.To continuously strengthen learning, improve their comprehensive quality. 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Over the past year, through continuous learning and fumble, studied the gas generation, collection and methods, gradually familiar with and master the company introduced the working principle, operation method of gas machine. With the help of the department leaders and colleagues, familiar with and master the launch of the division principle, debugging method of the control system, and to wuhan Chen Guchong garbage power plant of gas machine control system transformation, learn to debug, accumulated some experience. All in all, over the past year, did some work, have also made some achievements, but the results can only represent the past, there are some problems to work, can't meet the higher requirements. In the future work, I must develop the oneself advantage, lack of correct, foster strengths and circumvent weaknesses, for greater achievements. Looking forward to XXXX years of work, I'll be more efforts, constant progress in their jobs, make greater achievements. 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The Extremely Red Objects Found Thus Far in the Caltech Faint Galaxy Redshift Survey

a rXiv:as tr o-ph/988343v13Aug1998The Extremely Red Objects Found Thus Far in the Caltech Faint Galaxy Redshift Survey 1Judith G.Cohen 2,David W.Hogg 3,4,5Roger Blandford 3,Michael A.Pahre 2,5,6&Patrick L.Shopbell 2ABSTRACT We discuss the very red objects found in the ﬁrst ﬁeld of the Caltech Faint Galaxy Redshift Survey,for which the observations and analysis are now complete.In this ﬁeld,which is 15arcmin 2and at J005325+1234there are 195objects with K s <20mag,of which 84%have redshifts.The sample includes 24spectroscopically conﬁrmed Galactic stars,136galaxies,three AGNs,and 32objects without redshifts.About 10%of the sample has (R −K )≥5mag.Four of these objects have redshifts,with 0.78≤z ≤1.23.Three of these are based on absorption features in the mid-UV,while the lowest redshift object shows the standard features near 4000˚A .Many of the objects still without redshifts have been observed spectroscopically,and no emission lines were seen in their spectra.We believe they are galaxies with z ∼1−1.5that are red due to their age and stellar content and not to some large amount of internal reddening from dust.Among the many other results from this survey of interest here is a determination of the median extinction in the mid-UV for objects with strong emission line spectra at z ∼1−1.3.The result is extinction by a factor of ∼2at 2400˚A .1.Introduction We have completed the analysis of the data for the ﬁrst ﬁeld of this survey,which is 2x 7.3arcmin 2ﬁeld at J005325+1234.The sample is selected ignoring morphology at K and consists of the 195objects with K <20mag in this ﬁeld.These were observed with the LowResolution Imaging Spectrograph(Oke et al.1995)at the Keck Observatory.Six color photometry (UBV RIK)is available for the entireﬁeld as well from Pahre et al.(1998).Redshifts were successfully obtained for163of the195objects in the sample to achievea completeness of84%.These redshifts lie in the range[0.173,1.44]and have a median of0.58(excluding24spectroscopically conﬁrmed Galactic stars).The sample includes two broad lined AGNs and one QSO.The objects are assigned to spectral classes based on the relative preponderance of emission lines versus absorption lines in their spectra.The four spectral classes used for extragalactic objects are“E”for emission line dominated spectra(33galaxies),“A”for absorption line dominated spectra(51galaxies),“C”for composite spectra(52galaxies),and“Q”for AGNs.A few starbursts were found,classiﬁed as“B”,but for the present discussion they are grouped together with the emission line galaxies.2.Rest Frame Spectral Energy DistributionsThe galaxy rest frame SEDs derived from out UBV RIK photometry are very closely correlated to the galaxy spectral types.Both are also correlated with galaxy luminosity;blue galaxies show the signature of recent star formation in their spectra and are less luminous forz<0.8than red galaxies which show no evidence for recent star formation in their spectra. Representative SEDs are shown in Figure1.The SEDs for selected galaxies(D0K183,172,108, 188and158)with z>0.9shown in Figure1a are remarkablyﬂat(blue).Figure1b shows the SEDs for all the absorption line galaxies in the z=0.58peak;they have quite steep(red)spectra.2.1.The Extremely Red Objects in Our SampleThere are24Galactic stars in this sample,mostly M dwarfs or M subdwarfs.The reddest galactic star identiﬁed spectroscopically in thisﬁeld has(R−K)=4.6mag.There are19objects in this sample with(R−K)≥5mag,which we call the very red objects,and which we believe to be galaxies rather than Galactic stars.Four of these have redshifts,most of which are somewhat uncertain.Figure2shows the rest frame SEDs for the four very red galaxies with redshifts.The second panel of Figure2shows the SEDs for three of the very red objects which do not have redshifts,calculated assuming z=1.Redder than B,these look similar to those SEDs shown in theﬁrst panel of thisﬁgure,but the objects are somewhat fainter.Most of the U and B magnitudes for these objects are upper limits,as indicated by the vertical bars going downward from the relevant points.A more complete discussion of the redshift peaks(i.e.groups and poor clusters of galaxies), luminosity function,the cosmological volume density,the constraints on mergers,the ultraviolet extinction and other issues can be found in two papers,one of which has been submitted to ApJFig.1.—The rest frame spectral energy distributions(SEDs)for selected galaxies.The abscissa is the rest frequency and the rest wavelengths corresponding to our6color photometry augmented by the two supplementary ultraviolet bands P and Q(log(ν)=15.0and15.1)are indicated.The ordinate is the logarithm of the spectral power in units of both L∗B and W.Each galaxy SED shows the rest wavelengths corresponding to the observations and dashed lines are used to indicate extrapolations.The upper horizontal scale can be used in conjunction with the K point to measure the redshift of the galaxy.Fig. 2.—The rest frame SEDs for the four extremely red galaxies for which redshifts have been determined from our survey.The second panel shows the rest frame SEDs for three of the extremely red galaxies without redshifts,calculated assuming z=1.The line in the lower left indicates how the SEDs will shift for0.5<z<1.5.(Cohen et al.1998a)while the other(Cohen et al.1998b)will be published in ApJS.3.Final CommentsWe have determined the fraction of very red objects among our sample.For counts to K<20 mag,∼10%of the sample of195objects is very red,i.e.has(R−K)≥5mag.If one excludes the known Galactic stars from the sample,this fraction does not change substantially.We have examined the spectra of many of these extremely red objects and have succeeded in determining the redshifts of four of them,although the redshifts are not as certain as one might desire.We suggest that these are galaxies with z∼1−1.5in which reddening by dust is not playing a major role.In particular they are not heavily reddened starbursts.(If they were,we should have seen some moderately reddened emission line galaxies,and there were no such beasts among our sample).Instead we believe their extremely red colors are a direct consequence of their age,stellar composition,k-corrections,etc.and that these extremely red objects are the analogs at this redshift range of local elliptical galaxies.We thus support Persson et al.(1993)and Graham&Dey(1996),who among others,have speculated that such objects are passively-evolved elliptical galaxies with z>1.More work is going to be required to get someﬁrst class redshifts for these,or similar, hopefully brighter,objects,to establish their nature in a more deﬁnitive way.The entire Keck/LRIS user community owes a huge debt to Jerry Nelson,Gerry Smith,Bev Oke,and many other people who have worked to make the Keck Telescope and LRIS a reality. We are grateful to the W.M.Keck Foundation,and particularly its late president,Howard Keck, for the vision to fund the construction of the W.M.Keck Observatory.JGC is grateful for partial support from STScI/NASA grant AR-06337.12-94A.DWH and MAP were supported in part by Hubble Fellowship grants HF-01093.01-97A and HF-01099.01-97A from STScI(which is operated by AURA under NASA contract NAS5-26555).REFERENCESCohen,J.G.,Hogg,D.W.,Pahre,M.A.,Blandford,R.,Shopbell,P.L.&Richberg,K.,1998, ApJS,submittedCohen,J.G.,Blandford,R.,Hogg,D.W.,Pahre,M.A.&Shopbell,P.L.,1998,ApJ,submitted Graham,J.R.,&Dey,A.1996,ApJ,471,720Oke,J.B.,Cohen,J.G.,Carr,M.,Cromer,J.,Dingizian,A.,Harris,F.H.,Labrecque,S., Lucinio,R.,Schaal,W.,Epps,H.,&Miller,J.1995,PASP,107,307Pahre,M.A.,et al.1998,ApJS,submittedPersson,S.E.,McCarthy,P.J.,Dressler,A.,&Matthews,K.,1993,in The Evolution of Galaxies and their Environments,eds.D.Hollenbach,H.Thronson&J.M.Shull,NASA Conference Publication3190,69。

斑马技术公司DS8108数字扫描仪产品参考指南说明书

Chapter 1: Getting Started Introduction .................................................................................................................................... 1-1 Interfaces ....................................................................................................................................... 1-2 Unpacking ...................................................................................................................................... 1-2 Setting Up the Digital Scanner ....................................................................................................... 1-3 Installing the Interface Cable .................................................................................................... 1-3 Removing the Interface Cable .................................................................................................. 1-4 Connecting Power (if required) ................................................................................................ 1-4 Configuring the Digital Scanner ............................................................................................... 1-4

Royal Greenwich Observatory

Abstract.
2 supernovae can provide a distance indicator and \standard clock" to study the cosmological parameters q0 , , 0, and H0 . This presentation and the following presentations of Kim et al. (1996), Goldhaber et al. (1996), and Pain et al. (1996) will discuss observation strategies and rates, analysis and calibration issues, the sources of measurement uncertainty, and the cosmological implications, including bounds on q0 , of these rst high-redshift supernovae from our ongoing search.
then apply for the telescope time to study them, beginning at least a few days before maximum light. To solve these problems, we developed a new search technique. Figure 1 presents a schematic outline of the strategy. Just after a new moon, we observe many tens of high-galactic-latitude elds (including known highredshift clusters when possible) on a 2.5- to 4-meter telescope. With a wide- eld camera, each image contains hundreds of galaxies at redshifts 0.3 { 0.6. Just before the following new moon, we observe the same elds again. We compare the images, thus checking tens of thousands of high redshift galaxies (including those below our detection limit) to nd the ten or so showing the new light of a supernova that was not there on the previous observation. The supernovae generally do not have time to reach maximum light, with only 2.5 to 3 weeks (or approximately 11 to 14 days in the supernova rest frame) between our after- and before-new-

The evolution of clustering and bias in the galaxy distribution

a rXiv:as tr o-ph/98528v115May1998The evolution of clustering and bias in the galaxy distribution B y J.A.Peacock Institute for Astronomy,Royal Observatory,Edinburgh EH93HJ,UK This paper reviews the measurements of galaxy correlations at high redshifts,and discusses how these may be understood in models of hierarchical gravita-tional collapse.The clustering of galaxies at redshift one is much weaker than at present,and this is consistent with the rate of growth of structure expected in an open universe.If Ω=1,this observation would imply that bias increases at high redshift,in conﬂict with observed M/L values for known high-z clusters.At redshift 3,the population of Lyman-limit galaxies displays clustering which is of similar amplitude to that seen today.This is most naturally understood if the Lyman-limit population is a set of rare recently-formed objects.Knowing both the clustering and the abundance of these objects,it is possible to deduce em-pirically the ﬂuctuation spectrum required on scales which cannot be measured today owing to gravitational nonlinearities.Of existing physical models for the ﬂuctuation spectrum,the results are most closely matched by a low-density spa-tially ﬂat universe.This conclusion is reinforced by an empirical analysis of CMB anisotropies,in which the present-day ﬂuctuation spectrum is forced to have the observed form.Open models are strongly disfavoured,leaving ΛCDM as the most successful simple model for structure formation.2J.A.Peacockcommon parameterization for the correlation function in comoving coordinates:ξ(r,z)=[r/r0]−γ(1+z)−(3−γ+ǫ),(1.2) whereǫ=0is stable clustering;ǫ=γ−3is constant comoving clustering;ǫ=γ−1isΩ=1linear-theory evolution.Although this equation is frequently encountered,it is probably not appli-cable to the real world,because most data inhabit the intermediate regime of 1<∼ξ<∼100.Peacock(1997)showed that the expected evolution in this quasilin-ear regime is signiﬁcantly more rapid:up toǫ≃3.(b)General aspects of biasOf course,there are good reasons to expect that the galaxy distribution will not follow that of the dark matter.The main empirical argument in this direction comes from the masses of rich clusters of galaxies.It has long been known that attempts to‘weigh’the universe by multiplying the overall luminosity density by cluster M/L ratios give apparent density parameters in the rangeΩ≃0.2to0.3 (e.g.Carlberg et al.1996).An alternative argument is to use the abundance of rich clusters of galaxies in order to infer the rms fractional density contrast in spheres of radius8h−1Mpc. This calculation has been carried out several diﬀerent ways,with general agree-ment on aﬁgure close to(1.3)σ8≃0.57Ω−0.56m(White,Efstathiou&Frenk1993;Eke,Cole&Frenk1996;Viana&Liddle1996). The observed apparent value ofσ8in,for example,APM galaxies(Maddox,Efs-tathiou&Sutherland1996)is about0.95(ignoring nonlinear corrections,which are small in practice,although this is not obvious in advance).This says that Ω=1needs substantial positive bias,but thatΩ<∼0.4needs anti bias.Although this cluster normalization argument depends on the assumption that the density ﬁeld obeys Gaussian statistics,the result is in reasonable agreement with what is inferred from cluster M/L ratios.What eﬀect does bias have on common statistical measures of clustering such as correlation functions?We could be perverse and assume that the mass and lightﬁelds are completely unrelated.If however we are prepared to make the more sensible assumption that the light density is a nonlinear but local function of the mass density,then there is a very nice result due to Coles(1993):the bias is a monotonic function of scale.Explicitly,if scale-dependent bias is deﬁned asb(r)≡[ξgalaxy(r)/ξmass(r)]1/2,(1.4) then b(r)varies monotonically with scale under rather general assumptions about the densityﬁeld.Furthermore,at large r,the bias will tend to a constant value which is the linear response of the galaxy-formation process.There is certainly empirical evidence that bias in the real universe does work this way.Consider Fig.1,taken from Peacock(1997).This compares dimen-sionless power spectra(∆2(k)=dσ2/d ln k)for IRAS and APM galaxies.The comparison is made in real space,so as to avoid distortions due to peculiar veloc-ities.For IRAS galaxies,the real-space power was obtained from the the projectedThe evolution of galaxy clustering and bias3Figure1.The real-space power spectra of optically-selected APM galaxies(solid circles)and IRAS galaxies(open circles),taken from Peacock(1997).IRAS galaxies show weaker clustering, consistent with their suppression in high-density regions relative to optical galaxies.The relative bias is a monotonic but slowly-varying function of scale.correlation function:Ξ(r)= ∞−∞ξ[(r2+x2)1/2]dx.(1.5)Saunders,Rowan-Robinson&Lawrence(1992)describe how this statistic can be converted to other measures of real-space correlation.For the APM galaxies, Baugh&Efstathiou(1993;1994)deprojected Limber’s equation for the angular correlation function w(θ)(discussed below).These diﬀerent methods yield rather similar power spectra,with a relative bias that is perhaps only about1.2on large scale,increasing to about1.5on small scales.The power-law portion for k>∼0.2h Mpc−1is the clear signature of nonlinear gravitational evolution,and the slow scale-dependence of bias gives encouragement that the galaxy correlations give a good measure of the shape of the underlying massﬂuctuation spectrum.2.Observations of high-redshift clustering(a)Clustering at redshift1At z=0,there is a degeneracy betweenΩand the true normalization of the spectrum.Since the evolution of clustering with redshift depends onΩ,studies at higher redshifts should be capable of breaking this degeneracy.This can be done without using a complete faint redshift survey,by using the angular clustering of aﬂux-limited survey.If the form of the redshift distribution is known,the projection eﬀects can be disentangled in order to estimate the3D clustering at the average redshift of the sample.For small angles,and where the redshift shell being studied is thicker than the scale of any clustering,the spatial and angular4J.A.Peacockcorrelation functions are related by Limber’s equation(e.g.Peebles1980): w(θ)= ∞0y4φ2(y)C(y)dy ∞−∞ξ([x2+y2θ2]1/2,z)dx,(2.1)where y is dimensionless comoving distance(transverse part of the FRW metric is[R(t)y dθ]2),and C(y)=[1−ky2]−1/2;the selection function for radius y is normalized so that y2φ(y)C(y)dy=1.Less well known,but simpler,is the Fourier analogue of this relation:π∆2θ(K)=The evolution of galaxy clustering and bias5 ever,the M/L argument is more powerful since only a single cluster is required, and a complete survey is not necessary.Two particularly good candidates at z≃0.8are described by Clowe et al.(1998);these are clusters where signiﬁcant weak gravitational-lensing distortions are seen,allowing a robust determination of the total cluster mass.The mean V-band M/L in these clusters is230Solar units,which is close to typical values in z=0clusters.However,the comoving V-band luminosity density of the universe is higher at early times than at present by about a factor(1+z)2.5(Lilly et al.1996),so this is equivalent to M/L≃1000, implying an apparent‘Ω’of close to unity.In summary,the known degree of bias today coupled with the moderate evolution in correlation function back to z=1 implies that,forΩ=1,the galaxy distribution at this time would have to consist very nearly of a‘painted-on’pattern that is not accompanied by signiﬁcant mass ﬂuctuations.Such a picture cannot be reconciled with the healthy M/L ratios that are observed in real clusters at these redshifts,and this seems to be a strong argument that we do not live in an Einstein-de Sitter universe.(b)Clustering of Lyman-limit galaxies at redshift3The most exciting recent development in observational studies of galaxy clus-tering is the detection by Steidel et al.(1997)of strong clustering in the popula-tion of Lyman-limit galaxies at z≃3.The evidence takes the form of a redshift histogram binned at∆z=0.04resolution over aﬁeld8.7′×17.6′in extent.For Ω=1and z=3,this probes the densityﬁeld using a cell with dimensionscell=15.4×7.6×15.0[h−1Mpc]3.(2.3) Conveniently,this has a volume equivalent to a sphere of radius7.5h−1Mpc,so it is easy to measure the bias directly by reference to the known value ofσ8.Since the degree of bias is large,redshift-space distortions from coherent infall are small; the cell is also large enough that the distortions of small-scale random velocities at the few hundred km s−1level are also ing the model of equation (11)of Peacock(1997)for the anisotropic redshift-space power spectrum and integrating over the exact anisotropic window function,the above simple volume argument is found to be accurate to a few per cent for reasonable power spectra:σcell≃b(z=3)σ7.5(z=3),(2.4) deﬁning the bias factor at this scale.The results of section1(see also Mo& White1996)suggest that the scale-dependence of bias should be weak.In order to estimateσcell,simulations of synthetic redshift histograms were made,using the method of Poisson-sampled lognormal realizations described by Broadhurst,Taylor&Peacock(1995):using aχ2statistic to quantify the nonuni-formity of the redshift histogram,it appears thatσcell≃0.9is required in order for theﬁeld of Steidel et al.(1997)to be typical.It is then straightforward to ob-tain the bias parameter since,for a present-day correlation functionξ(r)∝r−1.8,σ7.5(z=3)=σ8×[8/7.5]1.8/2×1/4≃0.146,(2.5) implyingb(z=3|Ω=1)≃0.9/0.146≃6.2.(2.6) Steidel et al.(1997)use a rather diﬀerent analysis which concentrates on the highest peak alone,and obtain a minimum bias of6,with a preferred value of8.6J.A.PeacockThey use the Eke et al.(1996)value ofσ8=0.52,which is on the low side of the published range of ingσ8=0.55would lower their preferred b to 7.6.Note that,with both these methods,it is much easier to rule out a low value of b than a high one;given a singleﬁeld,it is possible that a relatively‘quiet’region of space has been sampled,and that much larger spikes remain to be found elsewhere.A more detailed analysis of several furtherﬁelds by Adelberger et al. (1998)in fact yields a biasﬁgure very close to that given above,so theﬁrstﬁeld was apparently not unrepresentative.Having arrived at aﬁgure for bias ifΩ=1,it is easy to translate to other models,sinceσcell is observed,independent of cosmology.For lowΩmodels, the cell volume will increase by a factor[S2k(r)dr]/[S2k(r1)dr1];comparing with present-dayﬂuctuations on this larger scale will tend to increase the bias.How-ever,for lowΩ,two other eﬀects increase the predicted densityﬂuctuation at z=3:the cluster constraint increases the present-dayﬂuctuation by a factor Ω−0.56,and the growth between redshift3and the present will be less than a factor of4.Applying these corrections givesb(z=3|Ω=0.3)The evolution of galaxy clustering and bias7 87GB survey(Loan,Lahav&Wall1997),but these were of only bare signiﬁcance (although,in retrospect,the level of clustering in87GB is consistent with the FIRST measurement).Discussion of the87GB and FIRST results in terms of Limber’s equation has tended to focus on values ofǫin the region of0.Cress et al.(1996)concluded that the w(θ)results were consistent with the PN91 value of r0≃10h−1Mpc(although they were not very speciﬁc aboutǫ).Loan et al.(1997)measured w(1◦)≃0.005for a5-GHz limit of50mJy,and inferred r0≃12h−1Mpc forǫ=0,falling to r0≃9h−1Mpc forǫ=−1.The reason for this strong degeneracy between r0andǫis that r0parame-terizes the z=0clustering,whereas the observations refer to a typical redshift of around unity.This means that r0(z=1)can be inferred quite robustly to be about7.5h−1Mpc,without much dependence on the rate of evolution.Since the strength of clustering for optical galaxies at z=1is known to correspond to the much smaller number of r0≃2h−1Mpc(e.g.Le F`e vre et al.1996),we see that radio galaxies at this redshift have a relative bias parameter of close to 3.The explanation for this high degree of bias is probably similar to that which applies in the case of QSOs:in both cases we are dealing with AGN hosted by rare massive galaxies.3.Formation and bias of high-redshift galaxiesThe challenge now is to ask how these results can be understood in cur-rent models for cosmological structure formation.It is widely believed that the sequence of cosmological structure formation was hierarchical,originating in a density power spectrum with increasingﬂuctuations on small scales.The large-wavelength portion of this spectrum is accessible to observation today through studies of galaxy clustering in the linear and quasilinear regimes.However,non-linear evolution has eﬀectively erased any information on the initial spectrum for wavelengths below about1Mpc.The most sensitive way of measuring the spectrum on smaller scales is via the abundances of high-redshift objects;the amplitude ofﬂuctuations on scales of individual galaxies governs the redshift at which these objectsﬁrst undergo gravitational collapse.The small-scale am-plitude also inﬂuences clustering,since rare early-forming objects are strongly correlated,asﬁrst realized by Kaiser(1984).It is therefore possible to use obser-vations of the abundances and clustering of high-redshift galaxies to estimate the power spectrum on small scales,and the following section summarizes the results of this exercise,as given by Peacock et al.(1998).(a)Press-Schechter apparatusThe standard framework for interpreting the abundances of high-redshift objects in terms of structure-formation models,was outlined by Efstathiou& Rees(1988).The formalism of Press&Schechter(1974)gives a way of calculating the fraction F c of the mass in the universe which has collapsed into objects more massive than some limit M:F c(>M,z)=1−erf δc2σ(M) .(3.1)8J.A.PeacockHere,σ(M)is the rms fractional density contrast obtained byﬁltering the linear-theory densityﬁeld on the required scale.In practice,thisﬁltering is usually performed with a spherical‘top hat’ﬁlter of radius R,with a corresponding mass of4πρb R3/3,whereρb is the background density.The numberδc is the linear-theory critical overdensity,which for a‘top-hat’overdensity undergoing spherical collapse is1.686–virtually independent ofΩ.This form describes numerical simulations very well(see e.g.Ma&Bertschinger1994).The main assumption is that the densityﬁeld obeys Gaussian statistics,which is true in most inﬂationary models.Given some estimate of F c,the numberσ(R)can then be inferred.Note that for rare objects this is a pleasingly robust process:a large error in F c will give only a small error inσ(R),because the abundance is exponentially sensitive toσ.Total masses are of course ill-deﬁned,and a better quantity to use is the velocity dispersion.Virial equilibrium for a halo of mass M and proper radius r demands a circular orbital velocity ofV2c=GMΩ1/2m(1+z c)1/2f 1/6c.(3.3)Here,z c is the redshift of virialization;Ωm is the present value of the matter density parameter;f c is the density contrast at virialization of the newly-collapsed object relative to the background,which is adequately approximated byf c=178/Ω0.6m(z c),(3.4) with only a slight sensitivity to whetherΛis non-zero(Eke,Cole&Frenk1996).For isothermal-sphere haloes,the velocity dispersion isσv=V c/√The evolution of galaxy clustering and bias9 and the more recent estimate of0.025from Tytler et al.(1996),thenΩHIF c=2for the dark halo.A more recent measurement of the velocity width of the Hαemission line in one of these objects gives a dispersion of closer to100km s−1(Pettini,private communication),consistent with the median velocity width for Lyαof140km s−1 measured in similar galaxies in the HDF(Lowenthal et al.1997).Of course,these ﬁgures could underestimate the total velocity dispersion,since they are dominated by emission from the central regions only.For the present,the range of values σv=100to320km s−1will be adopted,and the sensitivity to the assumed velocity will be indicated.In practice,this uncertainty in the velocity does not produce an important uncertainty in the conclusions.(3)Red radio galaxies An especially interesting set of objects are the reddest optical identiﬁcations of1-mJy radio galaxies,for which deep absorption-line spectroscopy has proved that the red colours result from a well-evolved stellar population,with a minimum stellar age of3.5Gyr for53W091at z=1.55(Dun-10J.A.Peacocklop et al.1996;Spinrad et al.1997),and4.0Gyr for53W069at z=1.43(Dunlop 1998;Dey et al.1998).Such ages push the formation era for these galaxies back to extremely high redshifts,and it is of interest to ask what level of small-scale power is needed in order to allow this early formation.Two extremely red galaxies were found at z=1.43and1.55,over an area 1.68×10−3sr,so a minimal comoving density is from one galaxy in this redshift range:N(Ω=1)>∼10−5.87(h−1Mpc)−3.(3.9) Thisﬁgure is comparable to the density of the richest Abell clusters,and is thus in reasonable agreement with the discovery that rich high-redshift clusters appear to contain radio-quiet examples of similarly red galaxies(Dickinson1995).Since the velocity dispersions of these galaxies are not observed,they must be inferred indirectly.This is possible because of the known present-day Faber-Jackson relation for ellipticals.For53W091,the large-aperture absolute magni-tude isM V(z=1.55|Ω=1)≃−21.62−5log10h(3.10) (measured direct in the rest frame).According to Solar-metallicity spectral syn-thesis models,this would be expected to fade by about0.9mag.between z=1.55 and the present,for anΩ=1model of present age14Gyr(note that Bender et al.1996have observed a shift in the zero-point of the M−σv relation out to z=0.37of a consistent size).If we compare these numbers with theσv–M V relation for Coma(m−M=34.3for h=1)taken from Dressler(1984),this predicts velocity dispersions in the rangeσv=222to292km s−1.(3.11) This is a very reasonable range for a giant elliptical,and it adopted in the following analysis.Having established an abundance and an equivalent circular velocity for these galaxies,the treatment of them will diﬀer in one critical way from the Lyman-αand Lyman-limit galaxies.For these,the normal Press-Schechter approach as-sumes the systems under study to be newly born.For the Lyman-αand Lyman-limit galaxies,this may not be a bad approximation,since they are evolving rapidly and/or display high levels of star-formation activity.For the radio galax-ies,conversely,their inactivity suggests that they may have existed as discrete systems at redshifts much higher than z≃1.5.The strategy will therefore be to apply the Press-Schechter machinery at some unknown formation redshift,and see what range of redshift gives a consistent degree of inhomogeneity.4.The small-scaleﬂuctuation spectrum(a)The empirical spectrumFig.2shows theσ(R)data which result from the Press-Schechter analysis, for three cosmologies.Theσ(R)numbers measured at various high redshifts have been translated to z=0using the appropriate linear growth law for density perturbations.The open symbols give the results for the Lyman-limit(largest R)and Lyman-α(smallest R)systems.The approximately horizontal error bars showThe evolution of galaxy clustering and bias11Figure2.Theradius R.Thecircles)Theredshifts2,4,...The horizontal errors correspond to diﬀerent choices for the circular velocities of the dark-matter haloes that host the galaxies.The shaded region at large R gives the results inferred from galaxy clustering.The lines show CDM and MDM predictions,with a large-scale normalization ofσ8=0.55forΩ=1orσ8=1for the low-density models.the eﬀect of the quoted range of velocity dispersions for aﬁxed abundance;the vertical errors show the eﬀect of changing the abundance by a factor2atﬁxed velocity dispersion.The locus implied by the red radio galaxies sits in between. The diﬀerent points show the eﬀects of varying collapse redshift:z c=2,4,...,12 [lowest redshift gives lowestσ(R)].Clearly,collapse redshifts of6–8are favoured12J.A.Peacockfor consistency with the other data on high-redshift galaxies,independent of the-oretical preconceptions and independent of the age of these galaxies.This level of power(σ[R]≃2for R≃1h−1Mpc)is also in very close agreement with the level of power required to produce the observed structure in the Lyman alpha forest(Croft et al.1998),so there is a good case to be made that theﬂuctu-ation spectrum has now been measured in a consistent fashion down to below R≃1h−1Mpc.The shaded region at larger R shows the results deduced from clustering data (Peacock1997).It is clear anΩ=1universe requires the power spectrum at small scales to be higher than would be expected on the basis of an extrapolation from the large-scale spectrum.Depending on assumptions about the scale-dependence of bias,such a‘feature’in the linear spectrum may also be required in order to satisfy the small-scale present-day nonlinear galaxy clustering(Peacock1997). Conversely,for low-density models,the empirical small-scale spectrum appears to match reasonably smoothly onto the large-scale data.Fig.2also compares the empirical data with various physical power spectra.A CDM model(using the transfer function of Bardeen et al.1986)with shape parameterΓ=Ωh=0.25is shown as a reference for all models.This appears to have approximately the correct shape,although it overpredicts the level of small-scale power somewhat in the low-density cases.A better empirical shape is given by MDM withΩh≃0.4andΩν≃0.3.However,this model only makes physical sense in a universe with highΩ,and so it is only shown as the lowest curve in Fig.2c,reproduced from theﬁtting formula of Pogosyan&Starobinsky(1995; see also Ma1996).This curve fails to supply the required small-scale power,by about a factor3inσ;loweringΩνto0.2still leaves a very large discrepancy. This conclusion is in agreement with e.g.Mo&Miralda-Escud´e(1994),Ma& Bertschinger(1994),Ma et al.(1997)and Gardner et al.(1997).All the models in Fig.2assume n=1;in fact,consistency with the COBE results for this choice ofσ8andΩh requires a signiﬁcant tilt forﬂat low-density CDM models,n≃0.9(whereas open CDM models require n substantially above unity).Over the range of scales probed by LSS,changes in n are largely degenerate with changes inΩh,but the small-scale power is more sensitive to tilt than to Ωh.Tilting theΩ=1models is not attractive,since it increases the tendency for model predictions to lie below the data.However,a tilted low-Ωﬂat CDM model would agree moderately well with the data on all scales,with the exception of the ‘bump’around R≃30h−1Mpc.Testing the reality of this feature will therefore be an important task for future generations of redshift survey.(b)Collapse redshifts and ages for red radio galaxiesAre the collapse redshifts inferred above consistent with the age data on the red radio galaxies?First bear in mind that in a hierarchy some of the stars in a galaxy will inevitably form in sub-units before the epoch of collapse.At the time ofﬁnal collapse,the typical stellar age will be some fractionαof the age of the universe at that time:age=t(z obs)−t(z c)+αt(z c).(4.1) We can rule outα=1(i.e.all stars forming in small subunits just after the big bang).For present-day ellipticals,the tight colour-magnitude relation only allows an approximate doubling of the mass through mergers since the termination ofThe evolution of galaxy clustering and bias13Figure3.The age of a galaxy at z=1.5,as a function of its collapse redshift(assuming an instantaneous burst of star formation).The various lines showΩ=1[solid];openΩ=0.3 [dotted];ﬂatΩ=0.3[dashed].In all cases,the present age of the universe is forced to be14 Gyr.star formation(Bower at al.1992).This corresponds toα≃0.3(Peacock1991).A non-zeroαjust corresponds to scaling the collapse redshift asapparent(1+z c)∝(1−α)−2/3,(4.2) since t∝(1+z)−3/2at high redshifts for all cosmologies.For example,a galaxy which collapsed at z=6would have an apparent age corresponding to a collapse redshift of7.9forα=0.3.Converting the ages for the galaxies to an apparent collapse redshift depends on the cosmological model,but particularly on H0.Some of this uncertainty may be circumvented byﬁxing the age of the universe.After all,it is of no interest to ask about formation redshifts in a model with e.g.Ω=1,h=0.7when the whole universe then has an age of only9.5Gyr.IfΩ=1is to be tenable then either h<0.5against all the evidence or there must be an error in the stellar evolution timescale.If the stellar timescales are wrong by aﬁxed factor,then these two possibilities are degenerate.It therefore makes sense to measure galaxy ages only in units of the age of the universe–or,equivalently,to choose freely an apparent Hubble constant which gives the universe an age comparable to that inferred for globular clusters.In this spirit,Fig.3gives apparent ages as a function of eﬀective collapse redshift for models in which the age of the universe is forced to be14 Gyr(e.g.Jimenez et al.1996).This plot shows that the ages of the red radio galaxies are not permitted very much freedom.Formation redshifts in the range6to8predict an age of close to 3.0Gyr forΩ=1,or3.7Gyr for low-density models,irrespective of whetherΛis nonzero.The age-z c relation is ratherﬂat,and this gives a robust estimate of age once we have some idea of z c through the abundance arguments.It is therefore14J.A.Peacockrather satisfying that the ages inferred from matching the rest-frame UV spectra of these galaxies are close to the aboveﬁgures.(c)The global picture of galaxy formationIt is interesting to note that it has been possible to construct a consistent picture which incorporates both the large numbers of star-forming galaxies at z<∼3and the existence of old systems which must have formed at very much larger redshifts.A recent conclusion from the numbers of Lyman-limit galaxies and the star-formation rates seen at z≃1has been that the global history of star formation peaked at z≃2(Madau et al.1996).This leaves open two possibilities for the very old systems:either they are the rare precursors of this process,and form unusually early,or they are a relic of a second peak in activity at higher redshift,such as is commonly invoked for the origin of all spheroidal components. While such a bimodal history of star formation cannot be rejected,the rareness of the red radio galaxies indicates that there is no diﬃculty with the former picture. This can be demonstrated quantitatively by integrating the total amount of star formation at high redshift.According to Madau et al.,The star-formation rate at z=4is˙ρ∗≃107.3h M⊙Gyr−1Mpc−3,(4.3) declining roughly as(1+z)−4.This is probably a underestimate by a factor of at least3,as indicated by suggestions of dust in the Lyman-limit galaxies(Pettini et al.1997),and by the prediction of Pei&Fall(1995),based on high-z element abundances.If we scale by a factor3,and integrate toﬁnd the total density in stars produced at z>6,this yieldsρ∗(z f>6)≃106.2M⊙Mpc−3.(4.4) Since the red mJy galaxies have a density of10−5.87h3Mpc−3and stellar masses of order1011M⊙,there is clearly no conﬂict with the idea that these galaxies are theﬁrst stellar systems of L∗size which form en route to the general era of star and galaxy formation.(d)Predictions for biased clustering at high redshiftsAn interesting aspect of these results is that the level of power on1-Mpc scales is only moderate:σ(1h−1Mpc)≃2.At z≃3,the correspondingﬁgure would have been much lower,making systems like the Lyman-limit galaxies rather rare.For Gaussianﬂuctuations,as assumed in the Press-Schechter analysis,such systems will be expected to display spatial correlations which are strongly biased with respect to the underlying mass.The linear bias parameter depends on the rareness of theﬂuctuation and the rms of the underlyingﬁeld asb=1+ν2−1δc(4.5)(Kaiser1984;Cole&Kaiser1989;Mo&White1996),whereν=δc/σ,andσ2is the fractional mass variance at the redshift of interest.In this analysis,δc=1.686is assumed.Variations in this number of order10 per cent have been suggested by authors who have studied theﬁt of the Press-Schechter model to numerical data.These changes would merely scale b−1by a small amount;the key parameter isν,which is set entirely by the collapsed。

好奇研星象的英语作文

Curiosity has always been a driving force behind human exploration and discovery. In the realm of astronomy,this innate desire to understand the cosmos has led to remarkable advancements in our knowledge of the universe.The English essay on the curiosity about celestial phenomena can delve into various aspects of this pursuit,from the early days of stargazing to the modern era of space exploration.In ancient times,people gazed at the night sky with wonder,trying to make sense of the celestial bodies they observed.The patterns they saw in the stars led to the creation of constellations,which were used for navigation,timekeeping,and even as a means to tell stories and pass on cultural knowledge.The essay could explore the significance of these early observations and how they shaped human understanding of the cosmos.As time progressed,so did our tools for observing the heavens.The invention of the telescope in the early17th century by Hans Lippershey marked a significant leap in astronomical research.The essay could discuss the impact of this invention on our understanding of the universe,highlighting the contributions of astronomers like Galileo Galilei,who used the telescope to observe the moons of Jupiter and the phases of Venus, challenging the geocentric model of the universe.The curiosity about celestial phenomena also led to the development of various theories and laws that govern the motion of celestial bodies.The essay could delve into the work of Sir Isaac Newton,who formulated the laws of motion and universal gravitation, providing a comprehensive framework for understanding the movements of planets and stars.In the20th century,our curiosity about the stars took us beyond our own solar system. The essay could discuss the contributions of astronomers like Edwin Hubble,who discovered the expansion of the universe and the existence of other galaxies beyond the Milky Way.This revelation opened up a whole new realm of questions and curiosity about the nature and origins of the cosmos.The advent of space exploration has further fueled our curiosity about celestial phenomena.The essay could explore the significance of manned and unmanned space missions,such as the Apollo moon landings and the Voyager spacecraft,which have provided us with unprecedented insights into our solar system and beyond. Moreover,the curiosity about stars has also led to the discovery of exoplanets and the ongoing search for extraterrestrial life.The essay could discuss the implications of these discoveries for our understanding of life in the universe and the potential for future exploration.In conclusion,the curiosity about celestial phenomena has been a catalyst for human progress in astronomy.From the early days of stargazing to the modern era of space exploration,our desire to understand the cosmos has led to remarkable discoveries and advancements.The essay could emphasize the importance of maintaining this curiosity and continuing to explore the mysteries of the universe.。

Metals in Star-Forming Galaxies at High Redshift

a rXiv:as tr o-ph/56285v113J un25From Lithium to Uranium:Elemental Tracers of Early Cosmic Evo-lution Proceedings IAU Symposium No.228,2005V.Hill,P.Fran¸c ois &F.Primas,eds.c 2005International Astronomical Union DOI:00.0000/X000000000000000X Metals in Star-Forming Galaxies at High Redshift Claus Leitherer Space Telescope Science Institute,3700San Martin Dr.,Baltimore,MD 21218,USA email:leitherer@ Abstract.The chemical composition of high-redshift galaxies is an important property that gives clues to their past history and future evolution.Measuring abundances in distant galaxies with current techniques is often a challenge,and the canonical metallicity indicators can often not be applied.I discuss currently available metallicity indicators based on stellar and interstellar absorption and emission lines,and assess their limitations and systematic uncertainties.Recent studies suggest that star-forming galaxies at redshift around 3have heavy-element abundances already close to solar,in agreement with predictions from cosmological models.Keywords.galaxies:abundances,galaxies:high-redshift,galaxies:starburst,ultraviolet:galax-ies2Claus Leithererparison between the observed spectrum of MS1512–cB58(solid)and two syn-thetic models with1/4Z⊙(lower;dashed)and Z⊙(upper;dotted).The models have continuous star formation,age100Myr,and Salpeter IMF between1and100M⊙.The stellar lines are weaker in the metal-poor model(from Leitherer et al.2001).3.Techniques—Restframe Optical versus UVAbundance determinations typically fall into two categories,either relying on indica-tors in the restframe optical,or on those in the restframe UV.The restframe optical wavelength region has traditionally been used to determine galaxy abundances from nebular emission lines.At a redshift of z=3,the restframe optical is observed in the near-infrared(IR)H and K bands.Spectroscopic observations of LBGs in the near-IR have become technically feasible(e.g.,Pettini et al.2001)but abundance analyses are still challenging.Only the strongest lines such as,e.g.,Hα,Hβ,[N II]λ6584,or[O III]λ5007are detectable at suﬃcient S/N.Even when good-quality spectra are available,the atmospheric windows usually restrict the wavelengths to a narrow range,which precludes commonly used techniques such as the classical R23strong-line method(McGaugh1991). The need for alternative variants of the classical strong-line method led Pettini&Pagel (2004)to readdress the usefulness of the N2and O3N2ratios.The former is deﬁned as the ratio[N II]λ6584over Hαand was recently discussed by Denicol´o et al.(2002);the latter includes the oxygen line for the ratio([O III]λ5007/Hβ)/([N II]λ6584/Hα)and was originally introduced by Alloin et al.(1979).After calibrating the two abundance indicators with a local H II region sample,Pettini&Pagelﬁnd that O3N2and N2predict O/H to within0.25dex and0.4dex at the2σconﬁdence level,respectively.The observed frame optical wavelength region corresponds to the restframe UV of LBGs.The UV contains few nebular emission lines in star-forming galaxies(Leitherer 1997)and has rarely been used for chemical composition studies in local galaxies of this type.Fig.1compares the UV spectrum of the LBG MS1512–cB58with theoretical spectra(Leitherer et al.2001).Three groups of lines can be distinguished:(i)Interstellar absorption lines,most of which are strong and heavily saturated.Only in very few cases can unsaturated absorption lines in LBGs be used for an abundance analysis.(ii)Broad stellar-wind lines with emission and blueshifted absorption.These lines are the telltales of massive OB stars whose stellar winds are metallicity dependent.(iii)Weak photospheric absorption lines which can only be seen in high-quality spectra.Abundance studies from stellar lines in restframe UV spectra must rely either on suitable template stars or on extensive non-LTE radiation-hydrodynamic models which are only beginning to become available(Rix et al.2004).Metals in High-z Galaxies3 4.The Chemical Composition of LBGsAn initial,rough estimate of the heavy-element abundances can be obtained from the equivalent widths of the strong UV absorption lines.Heckman et al.(1998)pointed out the close correlation of the Si IVλ1400and C IVλ1550equivalent widths with O/H in a sample of local star-forming galaxies.This correlation seems surprising,as these stellar-wind lines are deeply saturated.The reason for the metallicity dependence is the behavior of stellar winds in diﬀerent chemical environments.At lower abundance,the winds are weaker and have lower velocity,and the lines become weaker and narrower.As a result,the equivalent widths are smaller at lower O/H.If the same correlation holds at high redshift,the observed equivalent widths in LBGs suggest[O/H]≃–0.5(Leitherer 1999).A similar,somewhat weaker correlation exists between O/H and the equivalent widths of the strongest interstellar lines.This is even more unexpected because the equivalent widths of saturated lines have essentially no dependence on the column density N ion:W∝b[ln(N ion/b)]0.5.Therefore the correlation must be caused by the b factor, and therefore by velocity.More metal-rich galaxies are thought to host more powerful starbursts with correspondingly larger mechanical energy release by stellar winds and supernovae.The energy input leads to increased macroscopic turbulence and higher gas velocities at higher O/H(Heckman et al.1998).If the same applies to star-forming galaxies in the high-redshift universe,their measured equivalent widths again indicate an oxygen abundance of about1/3the solar value.Pettini et al.(2001)determined oxygen abundances inﬁve LBGs from emission lines in restframe optical spectra.The redshift range of the sample dictated the use of the R23 method.The galaxies turned out to be rather metal-rich,with O/H somewhat below the solar value.This is roughly in agreement with restframe UV results,and an order of magnitude above the metallicities found in damped Lyman-αabsorbers(DLA)which are found at the same redshift.Because of the double-valued nature of the R23method, the possibility exists but is deemed less likely that the sample has oxygen abundances of only1/10the solar value.The lensed LBG MS1512–cB58and its bright restframe UV spectrum can be studied at suﬃciently high S/N and resolution to detect and resolve faint,unsaturated interstellar absorption lines.Pettini et al.(2002)measured numerous transitions from H to Zn cov-ering several ionization stages.Abundances of several key elements could be derived.The α-elements O,Mg,Si,P,and S all have abundances of about40%solar,indicating that the interstellar medium is highly enriched in the chemical elements produced by type II supernovae.In contrast,N and the Fe-peak elements Mn,Fe,and Ni are all less abundant than expected by factors of several.In standard chemical evolution models,most of the nitrogen is produced by intermediate-mass stars,whereas type Ia supernovae contribute most of the Fe-peak elements.Since the evolutionary time scales of intermediate-and low-mass stars are signiﬁcantly longer than those of massive stars producing theα-elements, the release of N and the Fe-group elements into the interstellar medium is delayed by ∼109yr.MS1512–cB58may be an example of a star-forming galaxy in its early stage of chemical enrichment,consistent with its cosmological age of only about15%of the age of the universe.Mehlert et al.(2002)provided similar arguments to explain variation of the C IVλ1550line relative to Si IVλ1400in a small sample of LBGs.C IV appears to decrease in strength relative to Si IV from lower to higher redshift,which may reﬂect the time delay of the carbon release by intermediate-mass stars.The interstellar lines in LBGs have blueshifts with velocities of up to several hun-dred km s−1indicating large-scale outﬂows.The associated galactic mass-loss rates of ∼102M⊙yr−1are comparable to the rates of star formation.The newly formed heavy4Claus LeithererFigure2.Left pair of panels:comparison of the observed spectrum of MS1512–cB58(thick) with fully synthetic spectra(thin)forﬁve diﬀerent metallicities,from twice solar to1/20solar. First panel:region around1425˚A;second:region of the Fe III blend near1978˚A.Each pair of panels is labeled with the metallicity of the synthetic spectrum shown.Right pair of panels: same as left pair,but for Q1307–BM1163(from Rix et al.2004).elements are removed from their birth sites by stellar winds and supernovae and are trans-ported into the halo and possibly into the intergalactic medium(Pettini et al.2002). Detailed studies of weak interstellar lines such as that done for MS1512–cB58remain a technical challenge,even for high-throughput spectrographs at the largest telescopes. Furthermore,the results for Fe-peak elements carry some uncertainty because of the a priori unknown depletion corrections.Abundance analyses using stellar lines are not aﬀected by depletion uncertainties.However,the existence of non-standard element ratios precludes the use of locally observed template spectra for spectral synthesis.Therefore our group(F.Bresolin,R.Kudritzki,C.Leitherer,M.Pettini,S.Rix)has embarked on a project to model the spectra of hot stars and link them with a spectral synthesis code to predict the emergent UV spectrum of a composite stellar population as a function of metallicity.We generated a grid of hydrodynamic non-LTE atmospheres with the WM-basic code(Pauldrach et al.2001)and calculated the corresponding UV line spectra.The resulting library was incorporated into the Starburst99code(Leitherer et al.1999)which then allowed us to compute a suite of model spectra for appropriate stellar population parameters.As aﬁrst application,we used several faint stellar blends around1425˚A and 1978˚A as a metallicity indicator(Rix et al.2004).The1425˚A feature is a blend of Si III, C III,and Fe V,and the1978˚A absorption is mainly Fe III.The synthesized spectra for ﬁve metallicities are compared to the observed restframe UV spectra of MS1512–cB58 and Q1307–BM1163in Fig.2.The model having40%solar metal abundance provides the bestﬁt to the data,in agreement with the results from other methods.A variety of independent techniques lead to consistent results for the chemical com-position of LBGs.While each method by itself is subject to non-negligible uncertainties,Metals in High-z Galaxies5Figure3.Metallicity-luminosity relationship.Data for local spiral and irregular galaxies are from Garnett(2002).The z=2objects are overluminous for their(O/H)abundances,derived using the N2calibration of Pettini&Pagel(2004)but lie closer to the relationship for the local galaxies than z=3LBGs(from Shapley et al.2004).the overall agreement of the results gives conﬁdence in the derived abundances.LBGs at z≃3have heavy-element abundances of about1/3the solar value.5.Cosmological PerspectiveStar-forming galaxies at z≃3,at an epoch when the universe’s age was only15% the present value,display a high level of chemical enrichment.What does their chemical composition tell us about their relation to other galaxies at lower redshift and to other structures found at z=3?Galaxies at somewhat lower redshift have only recently become accessible for detailed study due to the combined challenges of instrumentation and the galactic spectral prop-erties.Shapley et al.(2004)obtained K-band spectroscopy of seven UV-selected star-forming galaxies at redshifts between2and2.5.The N2method calibrated by Pettini &Pagel(2004)was used as an abundance diagnostic.When compared to the original higher-z LBGs,the z≃2sample is more metal-rich.This can be seen in Fig.3,where O/H of the z=2galaxies is compared with that of LBGs at z≃3and of local star-forming galaxies over a range of blue luminosities.The latter were analyzed with the R23method.The z=2sample has almost solar chemical composition but is still less metal-rich than local late-type galaxies with comparable luminosities.As a caveat,the comparison rests on the assumption that the N2and R23calibrations have no signiﬁcant oﬀset.The diﬀerence between the average redshift of the LBG sample and of the z=2 galaxies translates into a mean age diﬀerence of about1Gyr.Both the chemical proper-ties and the masses of the z=2galaxies and LBGs are consistent with standard passive evolution models.Kewley&Kobulnicky(2005)followed the metallicity evolution of star-forming galaxies with comparable luminosities from z=0to3.5.O/H was determined from restframe optical emission lines using the strong-line method in four homogeneous galaxy samples. The samples were taken from the CfA2survey,from the GOODSﬁeld,from Shapley et al.(2004),and from the LBG sample,covering z≈0,0.7,2.1−2.5,and2.5−3.5, respectively.The average oxygen abundance in the local universe,as deﬁned by the CfA2 sample is about solar.O/H decreases with redshift to approximately1/3solar at z=3.6Claus LeithererIt is instructive to compare the heavy-element abundances of LBGs to those of DLAs and to the Lyman-forest at the same redshift(Pettini2004).DLA systems have metallic-ities of about1/15Z⊙and are thought to be the cross sections of the outer regions and halos of(proto)-galaxies seen along the sightlines of quasars.Although the properties of LBGs and DLAs do not immediately support a close relation between the two classes of objects,at least some link seems likely.If so,the observed outﬂows in LBGs may provide the metal enrichment of the halos.The Lyman-forest is predicted by cold dark matter models to result from structure formation in the presence of an ionizing background. The Lyman-forest had long been thought to be truly primordial,but metal enrichment of1/100–1/1000Z⊙has recently been detected(Aguirre et al.2004).This relatively high metal abundance early in the evolution of the universe could have been produced by aﬁrst generation of Population III stars.Such stars can account for the amount of metals,and at the same time could have provided copious ionizing photons,as metal and photon production are closely correlated.Alternatively,star-forming galaxies at high redshift could be the production sites of the metals seen in the intergalactic medium if superwinds are capable of removing the newly formed metals from galactic disks. AcknowledgementsI would like to thank Max Pettini for a careful reading of the manuscript and for providing invaluable comments.ReferencesAguirre,A.,Schaye,J.,Kim,T.,Theuns,T.,Rauch,M.,&Sargent,W.2004,ApJ,602,38 Alloin,D.,Collin-Souﬀrin,S.,Joly,M.,&Vigroux L.1979,A&A,78,200Denicol´o,G.,Terlevich,R.,&Terlevich,E.2002,MNRAS,330,69Garnett,D.R.2002,ApJ,581,1019Giavalisco,M.2002,ARAA,40,579Heckman,T.M.,Robert,C.,Leitherer,C.,Garnett,D.,&van de Rydt,F.1998,ApJ,503,646 Kewley,L.,&Kobulnicky,H.A.2005,in R.de Grijs&R.M.Gonz´a lez Delgado(eds.),Star-bursts:From30Doradus to Lyman Break Galaxies,(Dordrecht:Springer),p.307 Kulkarni,V.P.,Fall,S.M.,Lauroesch,J.T.,York,D.G.,Welty,D.E.,Khare,P.,&Truran, J.W.2005,ApJ,618,68Leitherer,C.1997,in:W.H.Waller,M.N.Fanelli,J.E.Hollis,&A.C.Danks(eds.),The Ultraviolet Universe at Low and High Redshift:,(Woodbury:AIP),p.119Leitherer,C.1999,in:J.Walsh&M.Rosa(eds.),Chemical Evolution from Zero to High Redshift, (Berlin:Springer),p.204Leitherer,C.,Le˜a o,J.R.S.,Heckman,T.M.,Lennon,D.J.,Pettini,M.,&Robert,C.2001, ApJ,550,724Leitherer,C.,et al.1999,ApJS,123,3McGaugh,S.1991,ApJ,380,140Mehlert,D.,et al.2002,A&A,393,809Pauldrach,A.W.A.,Hoﬀmann,T.L.,&Lennon,M.2001,A&A,375,161Pettini,M.2004,in:C.Esteban,R.J.Garc´ıa L´o pez,A.Herrero,&F.S´a nchez(eds.),Cosmo-chemistry,XIII Canary Islands Winter School,(Cambridge:CUP),p.257Pettini,M.,Rix,S.A.,Steidel,C.C.,Adelberger,K.L.,Hunt,M.P.,&Shapley,A.E.2002, ApJ,569,742Pettini,M.,Shapley,A.E.,Steidel,C.C.,Cuby,J.,Dickinson,M.,Moorwood,A.F.M., Adelberger,K.L.,&Giavalisco,M.2001,ApJ,554,981Rix,S.A.,Pettini,M.,Leitherer,C.,Bresolin,F.,Kudritzki,R.,&Steidel,C.C.2004,ApJ, 615,98Shapley,A.E.,Erb,D.K.,Pettini,M.,Steidel,C.C.,&Adelberger,K.L.2004,ApJ,612,108 Steidel,C.C.,Adelberger,K.L.,Giavalisco,M.,Dickinson,M.&Pettini,M.1999,ApJ,519,1。

TD信息元素详解

信息元素功能性定义作者：李欣目录目录 (1)信息元素功能性定义 (11)1 核心网信息元素 (11)1.1 CN Information elements (11)1.2 CN Domain System Information (11)1.3 CN Information info (11)1.4 IMEI (11)1.5 IMSI (GSM-MAP) (11)1.6 Intra Domain NAS Node Selector (11)1.7 Location Area Identification (12)1.8 NAS message (12)1.9 NAS system information (GSM-MAP) (12)1.10 Paging record type identifier (12)1.11 PLMN identity (12)1.12 PLMN Type (12)1.13 P-TMSI (GSM-MAP) (12)1.14 RAB identity (12)1.15 Routing Area Code (12)1.16 Routing Area Identification (13)1.17 TMSI (GSM-MAP) (13)2 UTRAN 移动信息元素 (13)2.1 Cell Access Restriction (13)2.2 Cell identity (13)2.3 Cell selection and re-selection info for SIB3/4 (13)2.4 Cell selection and re-selection info for SIB11/12 (13)2.5 Mapping Info (14)2.6 URA identity (14)3 UE 信息元素 (14)3.1 Activation time (14)3.2 Capability Update Requirement (14)3.3 Cell update cause (15)3.4 Ciphering Algorithm (15)3.5 Ciphering mode info (15)3.6 CN domain specific DRX cycle length coefficient (15)3.7 CPCH Parameters (15)3.8 C-RNTI (15)3.9 DRAC system information (15)3.10 Void (16)3.11 Establishment cause (16)3.12 Expiration Time Factor (16)3.13 Failure cause (16)3.14 Failure cause and error information (16)3.15 Initial UE identity (16)3.16 Integrity check info (16)3.17 Integrity protection activation info (17)3.18 Integrity protection Algorithm (17)3.19 Integrity protection mode info (17)3.20 Maximum bit rate (17)3.21 Measurement capability (17)3.22 Paging cause (17)3.23 Paging record (17)3.24 PDCP capability (17)3.25 Physical channel capability (18)3.26 Protocol error cause (18)3.27 Protocol error indicator (18)3.28 RB timer indicator (18)3.29 Redirection info (18)3.30 Re-establishment timer (18)3.31 Rejection cause (18)3.32 Release cause (18)3.33 RF capability FDD (19)3.34 RLC capability (19)3.35 RLC re-establish indicator (19)3.36 RRC transaction identifier (19)3.37 Security capability (19)3.38 START (19)3.39 Transmission probability (19)3.40 Transport channel capability (20)3.41 UE multi-mode/multi-RAT capability (20)3.42 UE radio access capability (20)3.43 UE Timers and Constants in connected mode (21)3.44 UE Timers and Constants in idle mode (21)3.45 UE positioning capability (21)3.46 URA update cause (21)3.47 U-RNTI (21)3.48 U-RNTI Short (21)3.49 UTRAN DRX cycle length coefficient (21)3.50 Wait time (21)3.51 UE Specific Behavior Information 1 idle (21)3.52 UE Specific Behavior Information 1 interRAT (22)4 无线承载信息元素 (22)4.0 Default configuration identity (22)4.1 Downlink RLC STATUS info (22)4.2 PDCP info (22)4.3 PDCP SN info (22)4.4 Polling info (22)4.5 Predefined configuration identity (23)4.6 Predefined configuration value tag (23)4.7 Predefined RB configuration (23)4.8 RAB info (23)4.9 RAB info Post (23)4.10 RAB information for setup (23)4.11 RAB information to reconfigure (24)4.12 NAS Synchronization indicator (24)4.13 RB activation time info (24)4.14 RB COUNT-C MSB information (24)4.15 RB COUNT-C information (24)4.16 RB identity (24)4.17 RB information to be affected (24)4.18 RB information to reconfigure (25)4.19 RB information to release (25)4.20 RB information to setup (25)4.21 RB mapping info (25)4.22 RB with PDCP information (25)4.23 RLC info (25)4.24 Signaling RB information to setup (26)4.25 Transmission RLC Discard (26)5 传输信道信息元素 (26)5.1 Added or Reconfigured DL TrCH information (26)5.2 Added or Reconfigured UL TrCH information (27)5.3 CPCH set ID (27)5.4 Deleted DL TrCH information (27)5.5 Deleted UL TrCH information (27)5.6 DL Transport channel information common for all transport channels (27)5.7 DRAC Static Information (27)5.8 Power Offset Information (28)5.9 Predefined TrCH configuration (28)5.10 Quality Target (28)5.11 Semi-static Transport Format Information (28)5.12 TFCI Field 2 Information (28)5.13 TFCS Explicit Configuration (28)5.14 TFCS Information for DSCH (TFCI range method) (29)5.15 TFCS Reconfiguration/Addition Information (29)5.16 TFCS Removal Information (29)5.17 Void (29)5.18 Transport channel identity (29)5.19 Transport Format Combination (TFC) (29)5.20 Transport Format Combination Set (29)5.21 Transport Format Combination Set Identity (29)5.22 Transport Format Combination Subset (29)5.23 Transport Format Set (29)5.24 UL Transport channel information common for all transport channels (30)6 物理信道信息元素 (30)6.1 AC-to-ASC mapping (30)6.2 AICH Info (30)6.3 AICH Power offset (30)6.4 Allocation period info (30)6.5 Alpha (30)6.6 ASC Setting (30)6.7 Void (31)6.8 CCTrCH power control info (31)6.9 Cell parameters Id (31)6.10 Common timeslot info (31)6.11 Constant value (31)6.12 CPCH persistence levels (31)6.13 CPCH set info (31)6.14 CPCH Status Indication mode (31)6.15 CSICH Power offset (32)6.16 Default DPCH Offset Value (32)6.17 Downlink channelisation codes (32)6.18 Downlink DPCH info common for all RL (32)6.19 Downlink DPCH info common for all RL Post (32)6.20 Downlink DPCH info common for all RL Pre (32)6.21 Downlink DPCH info for each RL (32)6.22 Downlink DPCH info for each RL Post (33)6.23 Downlink DPCH power control information (33)6.24 Downlink information common for all radio links (33)6.25 Downlink information common for all radio links Post (33)6.26 Downlink information common for all radio links Pre (33)6.27 Downlink information for each radio link (33)6.28 Downlink information for each radio link Post (33)6.29 Void (33)6.30 Downlink PDSCH information (33)6.31 Downlink rate matching restriction information (34)6.32 Downlink Timeslots and Codes (34)6.33 DPCH compressed mode info (34)6.34 DPCH Compressed Mode Status Info (34)6.35 Dynamic persistence level (34)6.36 Frequency info (34)6.37 Individual timeslot info (35)6.38 Individual Timeslot interference (35)6.39 Maximum allowed UL TX power (35)6.40 Void (35)6.41 Midamble shift and burst type (35)6.42 PDSCH Capacity Allocation info (35)6.43 PDSCH code mapping (36)6.44 PDSCH info (36)6.45 PDSCH Power Control info (36)6.46 PDSCH system information (36)6.47 PDSCH with SHO DCH Info (36)6.48 Persistence scaling factors (36)6.49 PICH Info (36)6.50 PICH Power offset (37)6.51 PRACH Channelisation Code List (37)6.52 PRACH info (for RACH) (37)6.53 PRACH partitioning (37)6.54 PRACH power offset (37)6.55 PRACH system information list (37)6.56 Predefined PhyCH configuration (38)6.57 Primary CCPCH info (38)6.58 Primary CCPCH info post (38)6.59 Primary CCPCH TX Power (38)6.60 Primary CPICH info (38)6.61 Primary CPICH Tx power (38)6.62 Primary CPICH usage for channel estimation (38)6.63 PUSCH info (38)6.64 PUSCH Capacity Allocation info (38)6.65 PUSCH power control info (39)6.66 PUSCH system information (39)6.67 RACH transmission parameters (39)6.68 Radio link addition information (39)6.69 Radio link removal information (39)6.70 SCCPCH Information for FACH (39)6.71 Secondary CCPCH info (39)6.72 Secondary CCPCH system information (40)6.73 Secondary CPICH info (40)6.74 Secondary scrambling code (40)6.75 SFN Time info (40)6.76 SSDT cell identity (40)6.77 SSDT information (40)6.78 STTD indicator (40)6.79 TDD open loop power control (41)6.80 TFC Control duration (41)6.81 TFCI Combining Indicator (41)6.82 TGPSI (41)6.83 Time info (41)6.84 Timeslot number (41)6.85 TPC combination index (41)6.86 TSTD indicator (41)6.87 TX Diversity Mode (41)6.88 Uplink DPCH info (41)6.89 Uplink DPCH info Post (42)6.90 Uplink DPCH info Pre (42)6.91 Uplink DPCH power control info (42)6.92 Uplink DPCH power control info Post (42)6.93 Uplink DPCH power control info Pre (42)6.94 Uplink Timeslots and Codes (42)6.95 Uplink Timing Advance (42)6.96 Uplink Timing Advance Control (43)7 测量信息元素 (43)7.1 Additional measurements list (43)7.2 Cell info (43)7.3 Cell measured results (43)7.4 Cell measurement event results (44)7.5 Cell reporting quantities (44)7.6 Cell synchronization information (44)7.7 Event results (44)7.8 FACH measurement occasion info (45)7.9 Filter coefficient (45)7.10 HCS Cell re-selection information (45)7.11 HCS neighboring cell information (45)7.12 HCS Serving cell information (45)7.13 Inter-frequency cell info list (46)7.14 Inter-frequency event identity (46)7.15 Inter-frequency measured results list (46)7.16 Inter-frequency measurement (46)7.17 Inter-frequency measurement event results (47)7.18 Inter-frequency measurement quantity (47)7.19 Inter-frequency measurement reporting criteria (47)7.20 Inter-frequency measurement system information (47)7.21 Inter-frequency reporting quantity (47)7.22 Inter-frequency SET UPDATE (48)7.23 Inter-RAT cell info list (48)7.24 Inter-RAT event identity (48)7.25 Inter-RAT info (48)7.26 Inter-RAT measured results list (48)7.27 Inter-RAT measurement (49)7.28 Inter-RAT measurement event results (49)7.29 Inter-RAT measurement quantity (49)7.30 Inter-RAT measurement reporting criteria (49)7.31 Inter-RAT measurement system information (50)7.32 Inter-RAT reporting quantity (50)7.33 Intra-frequency cell info list (50)7.34 Intra-frequency event identity (50)7.35 Intra-frequency measured results list (50)7.36 Intra-frequency measurement (50)7.37 Intra-frequency measurement event results (51)7.38 Intra-frequency measurement quantity (51)7.39 Intra-frequency measurement reporting criteria (51)7.40 Intra-frequency measurement system information (51)7.41 Intra-frequency reporting quantity (52)7.42 Intra-frequency reporting quantity for RACH reporting (52)7.43 Maximum number of reported cells on RACH (52)7.44 Measured results (52)7.45 Measured results on RACH (52)7.46 Measurement Command (52)7.47 Measurement control system information (53)7.48 Measurement Identity (53)7.49 Measurement reporting mode (53)7.50 Measurement Type (53)7.51 Measurement validity (53)7.52 Observed time difference to GSM cell (53)7.53 Periodical reporting criteria (53)7.54 Primary CCPCH RSCP info (54)7.55 Quality measured results list (54)7.56 Quality measurement (54)7.57 Quality measurement event results (54)7.58 Quality measurement reporting criteria (54)7.59 Quality reporting quantity (54)7.60 Reference time difference to cell (54)7.61 Reporting Cell Status (55)7.62 Reporting information for state CELL_DCH (55)7.63 SFN-SFN observed time difference (55)7.64 Time to trigger (55)7.65 Timeslot ISCP info (55)7.66 Traffic volume event identity (55)7.67 Traffic volume measured results list (55)7.68 Traffic volume measurement (55)7.69 Traffic volume measurement event results (56)7.70 Traffic volume measurement object (56)7.71 Traffic volume measurement quantity (56)7.72 Traffic volume measurement reporting criteria (56)7.73 Traffic volume measurement system information (56)7.74 Traffic volume reporting quantity (56)7.75 UE internal event identity (56)7.76 UE internal measured results (57)7.77 UE internal measurement (57)7.78 UE internal measurement event results (57)7.79 UE internal measurement quantity (57)7.80 UE internal measurement reporting criteria (57)7.81 Void (58)7.82 UE Internal reporting quantity (58)7.83 UE Rx-Tx time difference type 1 (58)7.84 UE Rx-Tx time difference type 2 (58)7.85 UE Transmitted Power info (58)7.86 UE positioning Ciphering info (58)7.87 UE positioning Error (58)7.88 UE positioning GPS acquisition assistance (59)7.89 UE positioning GPS almanac (59)7.90 UE positioning GPS assistance data (59)7.91 UE positioning GPS DGPS corrections (59)7.92 UE positioning GPS ionospheric model (59)7.93 UE positioning GPS measured results (59)7.94 UE positioning GPS navigation model (60)7.95 UE positioning GPS real-time integrity (60)7.96 UE positioning GPS reference time (60)7.97 UE positioning GPS UTC model (61)7.98 UE positioning IPDL parameters (61)7.99 UE positioning measured results (61)7.100 UE positioning measurement (61)7.101 UE positioning measurement event results (61)7.102 Void (62)7.103 UE positioning OTDOA assistance data for UE-assisted (62)7.104 Void (62)7.105 UE positioning OTDOA measured results (62)7.106 UE positioning OTDOA neighbor cell info (62)7.107 UE positioning OTDOA quality (63)7.108 UE positioning OTDOA reference cell info (63)7.109 UE positioning position estimate info (64)7.110 UE positioning reporting criteria (64)7.111 UE positioning reporting quantity (64)7.112 T ADV info (65)8 其它信息元素 (65)8.1 BCCH modification info (65)8.2 BSIC (65)8.3 CBS DRX Level 1 information (65)8.4 Cell Value tag (65)8.5 Inter-RAT change failure (65)8.6 Inter-RAT handover failure (66)8.7 Inter-RAT UE radio access capability (66)8.8 Void (66)8.9 MIB Value tag (66)8.10 PLMN Value tag (66)8.11 Predefined configuration identity and value tag (66)8.12 Protocol error information (66)8.13 References to other system information blocks (66)8.14 References to other system information blocks and scheduling blocks (67)8.15 Rplmn information (67)8.16 Scheduling information (67)8.17 SEG COUNT (67)8.18 Segment index (67)8.19 SIB data fixed (67)8.20 SIB data variable (67)8.21 SIB type (67)8.22 SIB type SIBs only (67)9 ANSI-41 Information elements (68)10 Multiplicity values and type constraint values (68)信息元素功能性定义消息是由多个信息元素组合而成，信息元素根据其功能的不同划分为：核心网域信息元素、UTRAN 移动信息元素、UE 信息元素、无线承载信息元素、传输信道信息元素、物理信道信息元素和测量信息元素。

《星际探索AdAstra（2019）》英中字幕

不久的将来是充满希望和冲突的时代人类仰望星辰，寻找智慧的生命和进步的希望去超太空星际探索我很冷静，很稳定I'm calm, steady.我睡得很好，8.2小时，没有噩梦I slept well. 8.2 hours. No bad dreams.我准备好了，I am ready to go.努力做好工作，Ready to do my job to the best of my abilities. 专注于重要的事情I am focused only on the essential,排除无关因素to the exclusion of all else.做正确的决定I will make only pragmatic decisions.不让自己分心I will not allow myself to be distracted.不去想那些I will not allow my mind to linger无关紧要的事情on that which is unimportant.不要依赖其他人或事I will not rely on anyone or anything.不会被煽动犯错误I will not be vulnerable to mistakes.静息脉搏47 ，提交吧Resting BPM, 47. Submit.你的心理评估Your psychological evaluation已通过has been approved.有必要提醒As a reminder,请进行安全和设备检查……please perform any safety and equipment checks... 我一直想成为一名宇航员I always wanted to become an astronaut...为了全人类的未来for the future of mankind and all.至少我总是这么安慰自己At least, that's what I always told myself. 从外表看I see myself from the outside.我表现得……Smile, present a side.像没事一样微笑It's a performance...但是眼睛总盯在with my eye on the exit.出舱的路上Always on the exit.别碰我Just don't touch me.保重，少校。

Galaxy redshift surveys selected by neutral hydrogen using FAST

a r X i v :0707.2316v 2 [a s t r o -p h ] 15 A p r 2008Mon.Not.R.Astron.Soc.000,1–13(2007)Printed 15April 2008(MN L A T E X style ﬁle v2.2)Galaxy redshift surveys selected by neutral hydrogen usingthe Five-hundred metre Aperture Spherical TelescopeAlan R.Duﬀy,1,2Richard A.Battye,1Rod D.Davies,1Adam Moss,3Peter N.Wilkinson 11Jodrell Bank Observatory,School of Physics and Astronomy,University of Manchester,Macclesﬁeld,Cheshire SK119DL,U.K.2LeidenObservatory,Leiden University,PO Box 9513,2300RA Leiden,The Netherlands3Department of Physics and Astronomy,University of British Columbia,6224Agricultural Road,Vancouver,BC,V6T 1Z1,Canada12/07/2007ABSTRACTWe discuss the possibility of performing a substantial spectroscopic galaxy redshift survey selected via the 21cm emission from neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope (FAST)to be built in China.We consider issues related to the estimation of the source counts and optimizations of the survey,and discuss the constraints on cosmological models that such a survey could provide.We ﬁnd that a survey taking around 2years could detect ∼107galaxies with an average redshift of ∼0.15making the survey complementary to those already carried out at optical wavelengths.These conservative estimates have used the z =0HI mass function and have ignored the possibility of evolution.The results could be used to constrain Γ=Ωm h to 5%and the spectral index,n s ,to 7%independent of CMB data.If we also use simulated power spectra from the Planck satellite,one can constrain w to be within 5%of -1.Key words:telescopes –surveys –cosmological parameters –radio lines:galaxies1INTRODUCTIONGalaxy redshift surveys have played a signiﬁcant role in con-straining the cosmological model,with the largest surveys to date having been performed by the 2dFGRS 1and SDSS 2teams using optical techniques.Low redshift samples have been used for some time to derive constraints on cosmolog-ical parameter combinations Γand f b =Ωb /Ωm ,where Ωm and Ωb are the total matter and baryon densities deﬁned relative to critical,and h =H 0/(100km s −1Mpc −1),as well as the spectral index of the density ﬂuctuations,n s ,and neu-trino densities (Tegmark et al.2004a,b;Percival et al.2001;Cole et al.2005).More recently the SDSS team have used a more sparsely sampled,but larger volume survey of lumi-nous red galaxies (LRGs)to measure the expected baryon acoustic peak on scales of ∼100h −1Mpc (Eisenstein et al.2005).Since the acoustic scale is a standard ruler,this pro-vides a distance measurement allowing further constraints to be placed on cosmological parameters and,in particular,those which parametrize the properties of the dark energy.A large number of projects have been proposed recently to develop these ideas and to perform large photometric12dF homepage:.au/2dF 2SDSS homepage:surveys in the optical (and possibly the infra-red)wave-band to ﬁnd ∼108galaxies out to z ∼1(Dark Energy Survey;DES 3),as well as deeper spectroscopic surveys to ﬁnd ∼105galaxies at z ∼3(Blake and Glazebrook 2003).Such surveys will have much larger search volumes than those presently available,allowing for signiﬁcantly more ac-curate measurements of the power spectrum and hence of the acoustic scale at a variety of redshifts.This could lead to very tight constraints on the properties of the dark en-ergy.Another promising technique is to use the 21cm emission from neutral hydrogen (HI)as a tracer of the galaxies allowing for a spectroscopic galaxy redshift sur-vey (Abdalla and Rawlings 2004).This will require the de-velopment of telescopes with much higher survey speed,and hence a combination of larger collecting area and ﬁeld-of-view (FoV),than those available at present.The cur-rent state-of-the-art is a shallow all-sky survey;the com-bined HIPASS (Zwaan et al.2005)and HIJASS (Lang et al.2003)survey,which has found ∼104galaxies.Fortunately,a world-wide technology development programme is underway with the ultimate aim of building a Square Kilometre Ar-3DES homepage:2 A.R.Duﬀy et al.ray(SKA4)with collecting area∼106m2and a FoV muchgreater than1deg2,with these speciﬁcations the SKA sur-veys may detect∼109galaxies.Before the full SKA comes into operation(∼2020) another large radio telescope will have been constructed which also has great potential for HI surveys.The Five-hundred-metre Aperture Spherical Telescope(F AST)will be an Arecibo-like telescope with a signiﬁcantly larger aperture (∼500m)and FoV(Nan2006).The aim of this paper is todiscuss the scientiﬁc potential of a low-redshift HI survey of galaxies as a F AST key science programme.We will show that,if a focal plane array with100instantaneous beams can be developed,∼107galaxies can be detected within arealistic survey period(∼2years)and that the low-redshift galaxy power spectrum can be measured much more accu-rately than is currently possible with optical surveys.Sincehydrogen is the fundamental baryonic constituent of the uni-verse such a survey would provide an important view of the large-scale structure of the universe with diﬀerent biases andbe an important stepping stone to the larger HI galaxy sur-veys which will become possible with the SKA.In the next section we will brieﬂy discuss some relevantobservational parameters of F AST and then in subsequent sections,we will estimate the number counts,make fore-casts for errors on the power spectrum and constraints oncosmological parameters that could be possible with such a survey.2FIVE-HUNDRED-METRE APERTURE SPHERICAL TELESCOPE(F AST)The F AST telescope is funded and when completed in around2012-2013it will be the largest single dish tele-scope in the world.The expected speciﬁcations of the tele-scope(Nan2006)relevant to our discussion here are:•The prime-focus feed illuminates an area correspond-ing to a parabolic dish of diameter∼300m with apertureeﬃciency of70%giving A eﬀ=50000m2,•At21cm wavelength the beam width(FWHM)θ≈3 arcmin;the eﬀective pixel(equating the volume of a cube of height unity to the integral under a gaussian beam with the same height)has side1.064θand area1.133θ2.•The maximum observable zenith angle is of order40◦allowing the observation of≈50%of the full sky without signiﬁcant degradation of performance.Henceforth,the‘full sky’is deﬁned to be the maximum amount of sky accessible to the telescope i.e.≈20000deg2.•One of the principal receiver systems will be a focal plane array covering a frequency range around 1.4GHz (the21-cm HI line)which can produce n B instantaneous beams each with a system temperature T sys=25K(hence A eﬀ/T sys≈2000m2K−1per beam)and dual polarization capability.The expected thermal noise for a dual polarization single beam can be computed usingσnoise=√A eﬀ1∆νt,(1)4SKA homepage:/documents for an observing time of t and a frequency bandwidth of∆ν, where k=1380Jy m2K−1is the Boltzmann constant.If we assume a bandwidth of∆ν=1MHz which corresponds to a velocity linewidth of≈200km s−1at21cm then the instantaneous sensitivity of each beam of the F AST system will beσinst≈1mJy s1/2.The focal ratio of the telescope(f/D=0.47)restricts n B to 19for a conventional close-packed horn-based ar-ray,similar to that used for HIPASS and operated at the prime rger arrays require some of the horns to be far enough oﬀ-axis that aberration losses become unac-ceptable.A19-beam array gives an instantaneous FoV of Ωinst≈200arcmin2.We will use this19-beam system as theﬁducial benchmark for our basic calculations.A receiver array with n B∼100may well be possible.This require-ment could only be met with close-packed phased arrays of small antenna elements;these would not take up much more area than the19-beam horn system.The required phased ar-ray technology is actively being developed by several groups working within the international Square Kilometre Array R&D eﬀort5and hence we can be conﬁdent that by the time F AST comes into operation in2012-3the100-beam receiver capability will be available.This would allow for Ωinst≈(n B/19)200arcmin2.Such a system will be at least twice as sensitive per beam as that on the Arecibo Telescope and have a survey speed(Ωinst(A eﬀ/T sys)2)which is at least 6(n B/19)times faster than the7-beam system presently available there.F AST will also have more frequencyﬂexi-bility due to the excellent RFI enviroment at the F AST site and will be able to observe twice the area of the sky than does the Arecibo Telescope.3ESTIMATING GALAXY COUNTS3.1Properties of the HI galaxy distributionThe HI mass,M HI,of a galaxy at redshift z is given in terms of the observedﬂux,S,and line width,∆V o,by(Roberts 1975)M HI1+z d L(z)Jy∆V odzdΩ ∞M lim(z)dNdV dM=θ∗M∗HIαexp −MGalaxy redshift surveys selected by neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope3 We will,for the most part,assume no evolution in the HImass function out to the moderate redshifts appropriatefor a F AST survey and,therefore,use values of the pa-rameters derived from the most recent survey of the localuniverse(Zwaan et al.2005).In particular,we will chooseα=−1.37,θ∗=1.42×10−2h3Mpc−3and M∗HI=109.8M⊙.One can compute the average redshift of galaxies in the survey from N(M>M lim,z)by integrating appropriately over z,that is,z =∞0z N(M>M lim,z)dzkpc= M HI1+z.(7) A given object is detectable if itsﬂux density in bandwidth ∆ν=ν∆V o/c is greater than S lim.3.2Simple estimates assuming aﬁxed observingbandwidthA simple assumption,which should yield an order of magni-tude estimate of the number of objects that one might expect toﬁnd in a survey,is that the line width of all the galax-ies is∆V o=200km s−1.Under this assumption we have computed M lim(z)and the number of galaxies onewould Figure1.The angular sizes(in arc minutes)for galaxies with HI masses1010M⊙,dotted,109M⊙,dashed,and108M⊙,dot-dash. The(approximately)horizontal large-dashed line represents the FWHM beamsize of F AST which scales asλ∝1+z.617007000600170200060000175104 A.R.Duﬀy etal.Figure2.a)the S/N=4limiting mass for diﬀerent integrationtimes(in seconds)per pointing:t obs=6(dotted),60(short-dash),600(long-dash),6000(dot-short dash),60000(dot-longdash).b)the predicted number counts in a day of observation(deﬁned as18hours of on-source integration time)for each of theobservation strategies for n B=19.The bin width is∆z=0.01.The total number of galaxies predicted in each case is summa-rized in Table1.The solid line(that is,the lowest)in panel a)represents the estimated HI mass in a typical volume enclosedby the beam area and theﬁducial velocity width200km s−1.Ifthis line is greater than a substantive fraction(say,1/3)of themass limit one would expect a confusion related increase in theobserved noise.One can immediately scale the number counts discussedin the previous paragraph to longer integration times andlarger numbers of beams.If t survey is the total time of thesurvey and the focal plane array has n B beams then thenumber of galaxies detected at a particular signal-to-noiseratio is given byN(n B,t survey)= n B1d N(n B=19,t=1d),(8)although one has to be careful to make sure that t survey<t sky,the time taken to cover the entire sky available toF AST,which is given in terms of t obs byt sky n B t obscΩBdVGalaxy redshift surveys selected by neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope5lead to an increase in the eﬀective noise making it more diﬃcult to ﬁnd galaxies.From the above discussion it seems sensible to consider values of 60s <t obs <6000s ,in order to avoid any possible corrections to the statistics due to resolving galaxies at low z and confusion at high z .3.3Mass and inclination dependent eﬀects in the linewidthIn this section we attempt to improve our calculation of the number counts by taking into account the fact that not all galaxies have the same observed linewidth ∆V o .This can happen for two reasons:ﬁrst the intrinsic linewidth is expected to depend on the mass for virialized systems,and secondly not all galaxies will be observed edge-on.If they are observed face-on,then it is the motion of HI perpendicular to the disk which sets the linewidth and not rotation.The intrinsic linewidth of a galaxy,corrected for broad-ening,has been shown empirically to be related to the HI mass by (Briggs and Rao 1993;Lang et al.2003)∆V e1010M ⊙0.3,(11)although we note that this relation shows a large dispersion,especially for dwarf galaxies.The observed linewidth of a galaxy,∆V θ,which sub-tends an angle θbetween its spin axis and the line-of-sight can be computed using the Tully-Fouque rotation scheme (Tully and Fouque 1985)(∆V e sin(θ))2=(∆V θ)2+(∆V t )2−2∆V θ∆V t1−e−∆Vθ∆V c2.(12)∆V c =120km s −1represents an intermediate transition be-tween the small galaxies with Gaussian HI proﬁles in which the velocity contributions add quadratically and giant galax-ies with a ‘boxy’proﬁle reproduced by the linear addition of the velocity terms.∆V t ≈20km s −1is the velocity width due to random motions in the disk (Rhee and van Albada 1996;Verheijen and Sancisi 2001).With this deﬁnition of θ,θ=0corresponds to face-on and θ=π/2to edge-on.In cases where ∆V θ>>∆V c ,one can see that ∆V θ=∆V t +∆V e sin θ.For θ=0,one ﬁnds that ∆V θ=∆V t whereas for θ=π/2one ﬁnds that ∆V θ=∆V t +∆V e as expected.In addition there is a broadening eﬀect,∆V inst ,of the HI proﬁle due to the frequency resolution of the instrument,R .For a range of galaxy proﬁles,this broadening is found to be ∆V inst ≈0.55R (Bottinelli et al.1990).An appropriate value for the present discussion is ∆V inst ≈16km s −1.It has been shown (Lang et al.2003)that ∆V inst should be added linearly to ∆V θto give the eﬀective observed linewidth,∆V o (θ)=∆V θ+∆V inst .(13)∆V θcan be computed by using the Newton-Raphson method to ﬁnd the root of Eqn.12for a given ∆V e (M HI ).The eﬀective observed linewidth is illustrated in Fig.3as a function of ∆V e for an edge on galaxy and as function of θfor ∆V e =420km s −1.Figure 3.The eﬀective observed linewidth ∆V o as a function of a)∆V e for θ=π/2,that is edge on;b)θfor ∆V e =420km s −1.The limiting mass will now depend on θas well as z ,M lim (z,θ),since it will be easier to ﬁnd objects which have θ=0.In order to incorporate this we have take into account the probability of a given angle θ,P (θ),when computing the number counts N (M >M lim )=π/2dθP (θ)dNdθ=∆Ω∆zdVdV dMdM .(15)As an illustration,we have plotted dN/dθagainst cos θat z =0.1with ∆z =0.01for t obs =600s and S/N =46 A.R.Duﬀy etal.Figure 4.The eﬀect of the angle of inclination on the detectabil-ity of galaxies.We have used z =0.1,∆z =0.01,t obs =600s and S/N =4.in Fig.4which shows that objects with θclose to zero are preferentially selected.A simple assumption would be that the galaxies are ran-domly distributed on the celestial sphere and that the spin axes are also randomly distributed.This is not the case for satallite galaxies around their central galaxy,where a small anisotropy of the order of a few percent has been observed in SDSS data (Yang et al.2006),but it is likely to be a good approximation for the F AST surveys discussed here which will preferentially select large,well-separated galaxies with average separation ≈5Mpc.In this case P (θ)=sin θand therefore one can think of the value of cos θbeing uniformly distributed.Hence,one can deduce that N (M >M lim )=∆Ω∆zdVdV dM.(16)The results of taking account these eﬀects are presented in Table 2and Fig.5.It is clear that the number counts are slightly larger,by around 30%,than under the assumption that ∆V o =200km s −1.The scaling formulae discussed in section 3.2apply again here.For a survey with n B ≈100taking around 2years with t obs =600secs one would be able to cover all the sky available to F AST and ﬁnd ∼107galaxies.3.4Eﬀects of evolutionThe calculations of the previous section are based on the assumption that the HI mass function does not evolve.In this section we discuss the possible eﬀects of evolution on the number counts.It should be noted that none of these evolving models are used in the cosmological parameter con-straints in Section 4.The basic picture which we will put69500600280060000690Galaxy redshift surveys selected by neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope7 Figure5.The equivalent ofFig.2for the case of F AST with100beams when the eﬀects of mass and inclination on the observedlinewidth are taken into account.The eﬀects of including this mass evolution for areshown in Fig.6for the100-beam F AST with t obs=600s.Itis clear that evolution leads to an increase in the number ofgalaxies found per day which are14420,19070,25190,32780forβ=0,1,2,3and the median redshift increases withβ.Essentially,we have show that one can take the current pre-diction of∼107galaxies found by the100-beam F AST in2years of observation is a conservative lower bound.If we takeseriously the value ofβ=2then one would expect toﬁndnearly twice as many galaxies as in the case of no evolution.Prior to embarking on the full,all-sky galaxy redshiftsurvey,it would be sensible to perform an exploratory,deeper survey of a much smaller area,with the objectiveof measuring the evolution of the HI mass function.As wellFigure 6.The predicted daily number counts with S/N=4,∆z=0.01binwidth,for the F AST operating with n B=100and t obs=600s as a function of redshift with a simple redshift-evolving mass break in the Schechter function of Eqn.4.Thisis shown as a factorβ=[0,1,2,3]for the solid,dot,dash,dot-dashed lines respectively.as being of legitimate scientiﬁc interest in its own right sucha survey would allow one to investigate the optimal depth ofthe main redshift survey and pin-down some of the questionsraised in this section.In Fig.7we show the redshift distri-bution of galaxies that one would expect for an HI surveywith t obs=6000s lasting30d using the z=0mass func-tion and bins∆z=0.1.One would expected toﬁnd around42000galaxies with z ≈0.3using n B=19and222000for n B=100.In order to estimate accurately the parame-ters of the mass function,we estimate that one would require∼1000galaxies per bin.Therefore,we believe that it shouldbe possible to determine the HI mass function out to z≈0.6for n B=19and to z≈1n B=100with such a month-longsurvey.4EXPECTED ERRORS ON THE MATTERPOWER SPECTRUMWe now use the predicted galaxy number counts,assumingno evolution of the kind described in the last section,toestimate the errors of the galaxy power spectrum at z=z ≈0.15.P(k,z)is related to the power spectrum P(k,0)byP(k,z)=[D(z)]2P(k),(20)where D(z)is the growth factor computed fromD(z)=5Ωm[E(z′)]3,(21)an E(z)=H(z)/H0.Errors on the power spectrum are due to two factors:8 A.R.Duﬀy et al.Figure7.The number of galaxies that would be found in a surveylasting30d with t obs=6000s.In the case of n B=19one expecttoﬁnd around42000galaxies with z ≈0.3in17deg2,whereasone mightﬁnd as many as222000in87deg2for n B=100.Wehave used∆z=0.1and the z=0HI mass function in both cases.sample variance,i.e.the fact that not all k modes are mea-sured,and shot-noise which is the eﬀective noise on the mea-surement of an individual mode.The total errorσP on themeasurement of the power spectrum,P(k,z),for a givenk with logarithmic bin width∆(log k)can be expressedas(Feldman et al.1994;Tegmark1997)σP4πk3∆(log k)(2π)3nP 2,(22)where P=P(k,z)and n=n(z)is the number density ofgalaxies which are detected(making nP dimensionless)n(z)= ∞M lim(z)dN1+nP 2dVP lin(k),(25)1+Akto model the residual non-linear eﬀects on the original,lin-ear,power spectrum P lin(k).For the2dFGRS data,theauthors advocate using the parameters A=1.4Mpc−1and Q=4Mpc−2.We follow this treatment,and analyt-ically marginalize over the bias parameter b in the subse-quent Markov-Chain Monte-Carlo(MCMC)analysis.Forthe SDSS data,we use data presented in ref.(Tegmark et al.2004a),using19bandpowers in the range0.016<Galaxy redshift surveys selected by neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope 9δΩm /Ωm 0.4160.2210.2300.3100.078δf b /f b 0.3780.2530.4680.4860.283Table 3.Summary of parameter values which come from the SDSS main sample and 2dFGRS,and the simulated constraints expected from the proposed F AST surveys with :(i)n B =100,t obs =600s ;(ii)n B =19,t obs =120s ;(i)n B =19,t obs =600s .Values presented are the fractional errors for each parameter.0.010.110000.10.50.60.70.80.911.1Figure 8.a)the expected errors on the power spectrum for the proposed F AST survey;b)the same errors,but on a scale where the power spectrum has been divided by the equivalent no baryonmodel.Figure 9.The eﬀective V eﬀat k =0.075h Mpc −1for various completed and proposed surveys plotted against the approximate number of galaxies they have or might ﬁnd.The volumes are quoted in terms of that of the SDSS main galaxy sample which has V SDSS =1.5×108h −3Mpc 3.The open square is for the SDSS main sample,the cross is for the SDSS LRG sample,the hexagon is for the 2dFGRS,the pentagon is F AST with n B =19with t obs =600s while the circle is with t obs =120s and the open triangle is for the proposed F AST survey taking 2years with n B =100.k/(h Mpc −1)<0.205.We take the power spectrum of galax-ies to be of the form P obs (k )=b 2P lin (k ),and analyti-cally marginalize over the bias.For each of these datasets we use the window functions provided by (Cole et al.2005)and (Tegmark et al.2004a)respectively.For the F AST data,we generated a ﬁducial power spectrum using the CAMB software (Lewis et al.2000)using cosmological parameters that best-ﬁt the ΛCDM model (Spergel et al.2006),in this case [Ωc h 2,Ωb h 2,h ,n s ,A s ]are given by [0.104,0.0223,0.734,0.951,2.02×10−9],where A s is the initial amplitude of ﬂuctuations.We then sample P lin (k )at closely spaced values of k/h,from which we interpolate to obtain P lin (k )at the appropriate F AST survey k/h values,along with the simulated error bars.For completeness we have investigated three F AST sur-vey schemes,namely the ﬁducial 19-beam F AST,with in-10 A.R.Duﬀy et al.tegration times per pixel of t obs=120s and600secs, and the100-beam system with600seconds of integrationper pixel each of which would take∼2years to com-plete.For each scheme we use28bandpowers in the range 0.005<k/(hMpc−1)<0.155,and take the galaxy power spectrum to have the form P obs(k)=b2P lin(k).We also as-sume that the errors on each of the bins are uncorrelated due to the large binwidths taken in k as mentioned in Sec-tion4.The19-beam survey with t obs=120s,which could ﬁnd≈3×106,galaxies would cover the full20000deg2,al-beit to a shallower depth than the100-beam case,whereas the19-beam t obs=600s survey would only cover4000deg2 andﬁnd≈2×106galaxies.For the MCMC analysis we use COSMOMC(Lewis and Bridle2002)to create chains to estimate the conﬁdence limits on the cosmological param-eters.Since large parameter degeneracies exist when only including large-scale structure data in theﬁt,we impose the consistency relation that the angleθacoustic subtended by theﬁrst acoustic peak is1.040,which is strongly constrained by the WMAP3data(Spergel et al.2006). This essentially leaves three remaining free parameters in theﬁt:Ωc h2;Ωb h2and n s,which are used to compute the parameterΓ=Ωm h and f b=Ωb/Ωm.This is because we marginalize over bias,which absorbs the initial amplitude ofﬂuctuations,and h can then be derived from these parameters andθacoustic.In Table3we present the fractional error on each of the marginalized cosmological parameters for the2dFGRS and SDSS datasets,along with the three F AST observing schemes.The errorbars on f b are of a similarly poor level to those possible with2dFGRS and SDSS.This is probably since dependence of the power spectrum on f b is weak and the present surveys have reached the ceiling on how well this can be measured from the matter power spectrum.However, the errors onΓand n s are signiﬁcantly improved for the case of n B=100and t obs=600s,the area of the error ellipse in theΓ−n s direction is reduced by about a factor of six from that possible with2dFGRS.It is clear,however,that the F AST surveys with n B=19do not signiﬁcantly improve on the constraints already available.Of the two,that with t obs=120s which covers the whole sky does much better than t obs=600s making it clear,yet again,that surveys whichﬁnd the largest number of objects(and which cover all the available sky)will typically constrain cosmological parameters the best.In Fig.10we present marginalized2D likelihoods ofΓversus f b.Here,we impose a prior of n s=0.95±0.02,as preferred by the WMAP3data(Spergel et al.2006).The ﬁrst thing that is apparent is that the SDSS and2dFGRS do not agree on the central value;something which has been noted in the literature and is thought to be associated with the diﬀerent selection criteria for the two surveys(Cole et al. 2006).What is also evident is that F AST with n B=100per-forms considerably better than the two presently available surveys.Low redshift galaxy redshift surveys cannot constrain the properties of dark energy directly,but they can in com-bination with measurements of the CMB.Essentially,the measurement ofΓby the redshift survey breaks the angular diameter degeneracy,allowing simultaneous measurements of h and the equation-of-state parameter of the dark energy Ωb h20.0223±0.00020.0223±0.0002 n s0.952±0.0050.952±0.005 h0.751±0.1310.731±0.015 w−1.02±0.328−0.99±0.05Galaxy redshift surveys selected by neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope1Figure10.Cosmological parameter estimation for three surveys:the SDSS(top,blue);2dFGRS(middle,red)and the proposed100-beam F AST(bottom,yellow).Contours are1σand2σrespectively representing the68%and95%probability estimates.Due to thetension between the2dFGRS and SDSS central values,theﬁducial F AST cosmology was based on WMAP3.Note the large improvementin constraining this parameter space thanks to the order of magnitude increase in the number counts as well as in the volume probed.sented in Fig.11for a range of angular resolutions between6and24arcsec as a function of t obs.Included also for com-parison are predictions for F AST with19and100beams. Theﬁrst thing to notice is that the F AST curves are al-most straight lines which peak at the lowest possible valueof t obs conﬁrming our earlier assertion that the best observ-ing strategy for F AST,in terms of the number of objects de-tected,is to choose the value of t obs so that one would coverthe whole sky available to F AST in a deﬁned survey time. The curves for the10%SKA have a very diﬀerent shape,following a line similar to that for the F AST case for largevalues of t obs before eventually turning over and plumetting to zero.This is the eﬀect of theﬁnite resolution,with themaximum being where the majority of objects found in asurveyﬁll the beam exactly.It is clear to see that forθFWHM>15arcsec the10%SKA would make most of its detections in the point source regime for t obs>100s.A higher resolution is more likelyand if we consider the case of12arcsec resolution then theoptimum value of t obs≈1000s,but in terms of the number of objects found per day it is only marginally more powerfulthan for F AST with n B=100.For higher resolution stillthe optimal value of t obs increases to around2×104s≈6hours at6arcsec.In this case,one would be performing a much deeper survey which might capable of probing power spectrum at much higher redshifts and constraining the dark energy using the Baryonic Acoustic Oscillations.It would certainly be very diﬀerent in nature to that which we have proposed for F AST(Abdalla and Rawlings2004).To summarize if the10%stage of the SKA has relatively low resolution and a FoV of∼1deg2then it will be a factor of a few times more powerful than F AST,in terms of the number of galaxies found at relatively low redshifts.But if it has much higher angular resolution then the survey which it will yield will be dominated by objects at much higher redshifts.If this were to be the case the F AST and10% SKA would be complementary.7CONCLUSIONSIn this paper we have shown that the upcoming F AST is an extremely capable instrument for large-scale neutral hydro-gen surveys over the whole sky with the potential for large numbers of galaxies being discovered daily in the redshift range0−0.2and tens of galaxies out to mid-redshifts of order0.2−0.4.This would provide complementary infor-mation to the redshift surveys already performed at optical wavelengths and would be considerably better than those presently available(or likely to be available in the near fu-ture)selected using neutral hydrogen as the tracer.。

High-Redshift Galaxies The HDF and More

a rXiv:as tr o-ph/98383v19Mar1998High-Redshift Galaxies:The HDF and More Alberto Fern´a ndez-Soto 1,Kenneth nzetta 2,and Amos Yahil 21Dept.of Astrophysics and Optics,UNSW,Sydney,NSW2052,Australia 2Dept.of Physics and Astronomy,SUNY,Stony Brook,NY11794-3800,USA Abstract.We review our present knowledge of high-redshift galaxies,emphasizing particularly their physical properties and the ways in which they relate to present-day galaxies.We also present a catalogue of photometric redshifts of galaxies in the Hubble Deep Field and discuss the possibilities that this kind of study oﬀers to complete the standard spectroscopically based surveys.1Introduction For a long time models for galaxy formation and evolution advanced unhampered by observations.Nowadays,however,the rapid increase in both observational ca-pabilities and eﬃciency of the selection methods (see Steidel et al.1995[S95])has converted the task of looking for distant galaxies from one of the most diﬃ-cult challenges to an almost routine job,and large databases of high-z galaxies are already being compiled (Dickinson 1998,this Volume).Observations can now constrain the models,and this obliges us to understand the properties of these objects in order to get a complete image of the processes involved in the formation and evolution of galaxies.This study of the properties of high-z galaxies is twofold.We need to un-derstand the information provided by the conﬁrmed high-z galaxies.In this way we will learn about the spectral and morphological properties of the bright end of the galaxy population,i.e.,the putative progenitors of present-day large (L >L ∗)galaxies.Second,the use of photometric redshift techniques applied to deep multi-colour images (like the HDF,Williams et al.1996)opens a wealth of statistical methods to study those faint objects for which we cannot obtain spectroscopic information in the near future.These studies will yield further re-sults on the general distribution and evolution of galaxies.The main problem forboth methods resides in the z ≈1−2range,where spectroscopic identiﬁcation of galaxies at optical wavelengths is made diﬃcult by the lack of spectral features.2Physical Properties of the High-Redshift Galaxies We start with a brief review of the physical properties of high-z galaxies,most of which have been selected applying colour techniques (S95).The HDF trig-gered a wave of intense spectroscopic follow-up observation (Steidel et al.1996[S96],Lowenthal et al.1997[L97],Zepf et al.1996)that added a large number of galaxies to the sample.Nature also provides us with a telescope capable of2Alberto Fern´a ndez-Soto,Kenneth nzetta,and Amos YahilFig.1.Average spectrum of12high-redshift galaxies with z med=3.0(from L97). amplifying the light from distant galaxies,although plagued by geometric aber-rations:gravitational lensing has been used by several groups to discover some of the most distant known galaxies(Trager et al.1997[T97],Franx et al.1997).2.1Spectral Features:Dust,Metal and Gas ContentHigh-z galaxies(see Fig.1)are characterized by aﬂat continuum.Their Lyαemission lines vary considerably,from weak or even absent–with superposed damped absorption proﬁles–to rest EW of up to60˚A.All galaxies show optically thick Lyman limits and a strong discontinuity in the continuum bluewards of Lyα,due to the onset of the Lyαforest.Stellar and interstellar absorption lines are present,showing narrow proﬁles that are weaker for high-ionization species.A detailed study of the diﬀerent emission and absorption lines and the slopes of the observed spectra suggests that high-z galaxies are low metallicity systems (Z≈0.1Z⊙),with high neutral gas content that allows them to imprint damped HI absorption proﬁles on background objects.The amount of dust seems to be moderate(E(B−V)≈0.10),but a better measurement is necessary in order to establishﬁrmer values for the extinctions,luminosities and star formation rates.2.2Morphology and LuminosityMost of the observed galaxies show compact cores(with half-light radii on the order of a few kpc)surrounded by irregular asymmetric halos(Giavalisco et al. 1996[G96]).Although far from homogeneous,they look more regular than the galaxies observed at z≈1–only one of the galaxies at z>2shows the“chain”morphology reported by Cowie et al.(1995)to be usual in moderate-z galax-ies.A joint analysis of our photometric redshift catalogue and a morphological catalogue of galaxies in the HDF is presented by Simon Driver in this same Volume(see also Driver et al.1998[D98]).It must be remarked that we are ob-serving these objects in the rest-frame UV range,so passband eﬀects are indeedHigh-Redshift Galaxies:The HDF and More3 important.Direct comparison of their morphologies with those of their low-z counterparts will have to wait until high-resolution IR imaging is available.The total B-band luminosities lie in the range1−10L∗,with a strong con-centration in the compact,high surface brightness cores.The SFRs range from 1to50M⊙yr−1,although dust extinction might increase this by a factor of perhaps3or even more(Pettini et al.1997).2.3Number Densities and ClusteringSome measured number densities are:0.6±0.2(R<25.0,3.0<z<3.5,S95), 3.2±1.9(R<25.3,2.4<z<3.4,S96),6.5±2.0(R<25.5,2.0<z<3.5,L97). For the same ranges our catalogue gives0.6±0.3,3.2±0.8and7.7±1.2galaxies per square arc minute,respectively.We also estimate that approximately5,15 and25%of all galaxies brighter than AB(8140)=24,26and28respectively are at z>2.Evidence of large scale structure in the distribution of high-z galaxies is presented by Mark Dickinson in this Volume.3Photometric Redshifts in the HDFThe determination of redshift via photometric methods(the“Poor person’s z machine”,as stated in Koo1985)is a long-known technique.We present here some results from our catalogue,based on UBV IJHK photometry of the HDF –IR images provided by Mark Dickinson(Dickinson et al.1998in prep).Full details are given in Fern´a ndez-Soto et al.1998,(in prep).The catalogue is es-sentially complete down to AB(8140)=28and contains1067objects.Comparison with a sample of106spectroscopically determined redshifts shows that the results are very good up to z=1.4(∆z rms=0.13).At z>2 there is a7%rate of error(high-z galaxies that are assigned low redshift in our analysis),while for the rest we obtain∆z rms=nzetta et al.(1997)have shown that the number of wrong redshifts in the spectroscopic measurements (due to misidentiﬁcation of lines or operator error)are comparable to this rate.The advantage of this technique is the ability to estimate redshifts for large samples of objects that are too faint to have their redshifts spectroscopically measured(AB(8140)≈28vs.AB(8140)≈24).With our sample we can es-timate the N−m−z distribution,the Hubble Diagram for diﬀerent spectral types(see Fig.2),the morphological evolution of galaxies(see D98),SFR den-sities(Lanzetta et al.1998,in prep),and other characteristics.4Interpretation and ConclusionsThe available data allow for diﬀerent interpretations.While S95,S96and G96 support the hypothesis that the observed high-z galaxies are the progenitors of present-day luminous galaxies at the epoch of formation of theﬁrst stars in their spheroidal components,T97suggests that these objects will evolve to form4Alberto Fern´a ndez-Soto,Kenneth nzetta,and Amos YahilFig.2.Redshift distribution and Hubble Diagram of galaxies in the HDF.the Population II components of early-type spirals.Another interpretation(L97) maintains that these objects represent a range of physical processes and stages of galaxy formation and evolution rather than any particular class of object.While this third interpretation might be closer to reality,we are still missing an important piece of the puzzle.Detailed IR imaging and spectroscopy is needed in order to:a)shed light on the z=1−2galaxies allowing us to constrain evolutionary models;b)obtain images of the z>2galaxies at optical rest-frame wavelengths to be compared with their low-z counterparts and;c)perform moderate resolution spectroscopy of the z>2galaxies to accurately measure their metallicities and the importance of dust corrections.We expect that these observations,with the support of techniques like cos-mological simulations and stellar population evolutionary models,will lead us closer to the long-searched-for understanding of the process by which the Uni-verse came to be as we see it.Perhaps it is not the moment for us to“look deeper in the Southern Sky”,but to look at it with diﬀerent eyes.ReferencesCowie,L.L.,Hu,E.M.&Songaila,A.1995,AJ,110,1576Driver,S.P.et al.1998,ApJ,in pressFranx,M.et al.1997,ApJ,486,L75Giavalisco,M.,Steidel,C.C.&Macchetto,F.D.1996,ApJ,470,189Koo,D.C.1985,AJ,90,418Lanzetta,K.M.,Fern´a ndez-Soto,A.&Yahil,A.1997,in The Hubble Deep Field,eds.M.Livio,S.M.Fall&P.Madau(Cambridge,Cambridge University Press) Lowenthal,J.D.et al.1997,ApJ,481,673Pettini,M.et al.1997,in The ultraviolet Universe at low and high redshift,ed.W.Waller(Woodbury,AIP Press)Steidel,C.C.,Giavalisco,M.,Dickinson,M.&Adelberger,K.L.1996,AJ,112,352 Steidel,C.C.,Pettini,M.&Hamilton,D.1995,AJ,110,2519Trager,S.C.,Faber,S.M.,Dressler,A.&Oemler,A.1997,ApJ,485,92High-Redshift Galaxies:The HDF and More5 Williams,R.E.et al.1996,AJ,112,1335Zepf,S.E.,Moustakas,L.A.&Davis,M.1996,ApJ,474,L1。

The Hubble Ultra Deep Field

a r X i v :a s t r o -p h /0607632v 1 27 J u l 2006The Hubble Ultra Deep FieldSteven V.W.Beckwith 1,2,Massimo Stiavelli 1,Anton M.Koekemoer 1,John A.R.Caldwell 1,3,Henry C.Ferguson 1,Richard Hook 5,6,Ray A.Lucas 1,Louis E.Bergeron 1,Michael Corbin 7,Shardha Jogee 1,8,Nino Panagia 4,Massimo Robberto 4,Patricia Royle 1,Rachel S.Somerville 1,9,and Megan Sosey 1Space Telescope Science Institute,3700San Martin Drive,Baltimore,MD 21218,USAsvwb@ABSTRACTThis paper presents the Hubble Ultra Deep Field (HUDF),a one million second exposure of an 11square minute-of-arc region in the southern sky with the Advanced Camera for Surveys on the Hubble Space Telescope using Director’s Discretionary Time.The exposure time was divided among four ﬁlters,F435W (B 435),F606W (V 606),F775W (i 775),and F850LP (z 850),to give approximately uniform limiting magnitudes m AB ∼29for point sources.The image contains at least 10,000objects presented here as a catalog,the vast majority of which are galaxies.Visual inspection of the images shows few if any galaxies at redshifts greater than ∼4that resemble present day spiral or elliptical galaxies.The image reinforces the conclusion from the original Hubble Deep Field that galaxies evolved strongly during the ﬁrst few billion years in the infancy of the ing the Lyman break dropout method to derive samples of galaxies at redshifts between 4and 7,it is possible to study the apparent evolution of the galaxy luminosity function and number density.Examination of the catalog for dropout sources yields 504B 435-dropouts,204V 606-dropouts,and 54i 775-dropouts.The i 775-dropouts are most likely galaxies at redshifts between 6and ing these samples that are at diﬀerent redshifts but derived from the same data,we ﬁnd no evidence for a change in the characteristic luminosity of galaxies but some evi-dence for a decrease in their number densities between redshifts of 4and 7.Assessing the factors needed to derive the luminosity function from the data suggests there is considerable uncertainty in parameters from samples discovered with diﬀerent instruments and derived using independent assumptions about the source populations.This assessment calls into question some of the strong conclusions of recently published work on distant galaxies.The ultraviolet luminosity density of these samples is dominated by galaxies fainter than the characteristic luminosity,and the HUDF reveals considerably more luminosity than shallower surveys.The apparent ultraviolet luminos-ity density of galaxies appears to decrease from redshifts of a few to redshifts greater than 6,although this decrease may be the result of faint-end incompleteness in the most distant samples.The highest redshift samples show that star formation was already vigorous at the earliest epochs that galaxies have been observed,less than one billion years after the Big Bang.Subject headings:astronomical data bases:miscellaneous —cosmology:early universe —galaxies:evolution —galaxies:high-redshift6SpaceTelescope European Coordinating Facility7US Naval Observatory,FlagstaﬀStation 8University of Texas 9Max-Planck-Institut f¨u r Astronomie1.INTRODUCTIONA primary motivation for deep exposures of the sky has been to detect the most distant objects al-lowed by the observing technology.Over the last ten years,the use of ground-based telescopes com-bined with the Hubble Space Telescope produced large samples of galaxies at redshifts as high as5 to study early structure formation and the assem-bly of stars into present-day galaxies(Steidel et al. 1996a,b,1999;Ellis1998;Giavalisco2002).These programs successfully revealed the distant popula-tions recognized for several decades as important for understanding how the present-day universe came to be(Eggen et al.1962;Partridge and Pee-bles1967a,b;Tinsley1972a,b).Because of the complications arising from star formation,gas dy-namics,and feedback into the early intergalactic medium,theoretical predictions about the earliest galaxies are challenging,and the subject has been driven mainly by observations.Even though it has been possible to detect galaxies at redshifts above one,it has been diﬃ-cult to determine the redshifts and thus distances to objects from images only,where large samples may be rapidly assembled.Early workers rec-ognized that Lyαradiation should be especially prominent around theﬁrst generation of galax-ies,despite some uncertainty about the amount of scattering and absorption,and there should be a strong edge or break in the rest frame UV spec-tra at912˚A owing to absorption by hydrogen internal to the galaxies and in the intergalactic medium(e.g.Partridge1974;Davis&Wilkinson 1974;Koo&Kron1980.)Subsequently,Steidel and Hamilton(Steidel&Hamilton1992;Steidel 1996a,b)developed search techniques to exploit the Lyman edge using broad band colors toﬁnd galaxies with a paucity of short-wavelengthﬂux, the so-called“dropout”galaxies.This technique has proven most productive in discovering large samples of high redshift galaxies in multi-band im-ages.There are now samples of several thousand galaxies at redshifts between about2and5(Stei-del et al.1999,hereafter SAGDP99;Steidel et al. 2003;Giavalisco et al.2004.)When it became evident that the most dis-tant galaxies were characterized by compact high-surface brightness features(Driver et al.1995), the Hubble Space Telescope took a prominent role in the study of young galaxies.An important ad-vance came from the Hubble Deep Field(HDF; Williams et al.1996),a four-band,0.5million second exposure with the Wide Field Planetary Camera2.This seminal program using150orbits of Director’s Discretionary time on Hubble uncov-ered a large number of sources at redshifts above1 that would have been diﬃcult to discover from the ground.The HDF revealed a population of small, irregular galaxies that often appeared in pairs or small groups.Much of the light from these objects was high surface brightness—owing to high rates of star formation—but concentrated,requiring the resolution of Hubble to identify them as distant galaxies as opposed to red stars,say.Extension of the deepﬁeld approach to the southern hemi-sphere(Williams et al.2000)conﬁrmed the main conclusions of the HDF but also showed the limi-tations of a pencil beam survey in drawing broad conclusions about distant populations;cosmic er-ror within smallﬁelds can be substantial.Several advances since the HDF suggested that even deeper observations could reveal important aspects of the way that galaxies were created. The standard cosmology holds that the atoms in the universe were neutral following recombination at a redshift,z∼1100,until somewhere around z∼6−10,at which time they were reionized by stars and black holes.Theﬁrst observation of this epoch came with detection of the Gunn-Peterson hydrogen edge in the spectra of distant quasars discovered in the Sloan Digital Sky Survey(Becker et al.2001,Fan et al.2002),putting the redshift of complete reionization around6.The WMAP experiment made an indirect determination of a reionization era that started as early as redshift 11(Kogut et al.2003;Spergel et al.2003;Spergel et al.2006).Cold Dark Matter(CDM)models with a cosmological constant had some constraints that were not in accord with such an early epoch of reionization(Frenk et al.1985),although most of these models have suﬃcient freedom to accom-modate even the most discrepant data.Precise determination of the reionization history of the universe remains one of the important goals of ob-servational astronomy.The luminosity function inferred from the HDF suggested that searching a wider area to less depth than the HDF would be eﬃcient at picking up large populations of high redshift galaxies.Animportant advance since the HDF was the Great Observatories Origins Deep Survey:GOODS(Gi-avalisco et al.2004.)GOODS used the Advanced Camera for Surveys(ACS;Ford et al.2003) on Hubble to image an area thirty times larger but1magnitude shallower than the HDF.The GOODS sample contains more than60,000galax-ies with photometric magnitudes in four bands, B435(F445W),V606(F606W),i775(F775W),and z850(F850LP),and suﬃcient resolution to study structures as small as1kpc at redshifts approach-ing6.This sample is excellent for statistical stud-ies of bright galaxies at high redshifts.Deepﬁelds have an advantage over shallow ﬁelds to study the faint end of the luminosity func-tion and for increasing sample sizes when the slope of the luminosity function is large near the limit-ing magnitude of the survey.For a steep slope,the sample size will increase faster by investing addi-tional observing time in more exposure on a single ﬁeld rather than covering more area.The luminos-ity function at high redshifts is imprecise,but the current evidence indicates that it is consistent with a Schechter function(Schechter1976)with a char-acteristic luminosity,L∗,somewhat brighter than the local value and a faint end slope steep enough to warrant investment in a deepﬁeld(SAGDP99, Gabasch2004a,b.)The redshift at which the limiting magnitude of GOODS makes a deepﬁeld preferable to a wide ﬁeld can be estimated using a standard Schechter function.A deepﬁeld becomes preferable at a redshift greater than5,where the GOODS limit-ing magnitude is∼L∗,depending on the exact assumptions about how L∗evolves with redshift. The upper limit to the redshifts of the objects in a deep optical survey is when the Lyman edge goes beyond the longest wavelengthﬁlter.A practical limit for the ACS is when intergalactic absorp-tion shortward of Lyαshifts through the z850ﬁl-ter,z∼7.4.A deepﬁeld should produce samples of objects in the range5<z<7that are fainter than those found in GOODS and other wide sur-veys and allow a good characterization of the lu-minosity function in the early universe.It is most important to characterize the lu-minosity function below L∗to see the transition from exponential to power-law form,to measure the slope,and to assess the total luminosity of faint galaxies.The GOODS survey was limited to studying galaxies at the bright end of the lu-minosity function for redshifts greater than about 5.Even for lower redshifts,a deepﬁeld is use-ful to observe galaxies fainter than the character-istic brightness,providing important information about samples in the intermediate redshift ranges 2<z<5where much of the early star forma-tion in the universe took place.There is a strong degeneracy between derivations of object density and characteristic luminosity unless the luminos-ity function is well characterized below L∗.Such a degeneracy hampers the interpretation of shallow surveys even with large samples.As shown in the next section,it is possible to reach well below L∗out to redshifts near7with ACS on Hubble.This capability motivated a deep ACSﬁeld.The appearance of high redshift galaxies in the HDF and shallower surveys indicates substantial evolution in size and structure between early times and today.This evolution was already known at the time of the HDF,and subsequent observations tend to conﬁrm the conclusion that the galaxy populations look markedly diﬀerent at high red-shift compared to the present time.But the ap-parent morphology of high redshift galaxies is af-fected strongly by the loss of low-surface bright-ness features owing to cosmological dimming.An important way to test whether the loss of these features signiﬁcantly distorts our perception of galaxies at high redshift is to make deeper ob-servations of the sample at intermediate redshifts. Thus,an ultra deepﬁeld can provide an impor-tant complement to the pioneering observations of the HDF,GOODS,and ground-based surveys by searching for low-surface brightness components of faint galaxies.It was evident that a deepﬁeld with the new capabilities of Hubble following the installation of the ACS could address several important issues in early galaxy formation.In addition to augment-ing the samples of galaxies at redshifts greater than2,there was also the tantalizing possibility of pushing back the observational boundaries to redshifts greater than6to reach the reionization epoch.With these motivations in mind and fol-lowing the same philosophy pioneered by Robert Williams for the HDF,we held a series of meet-ings asking for advice on the scientiﬁc importance of another deepﬁeld and then assembled a Scien-tiﬁc Advisory Committee with a wide range of ex-pertise to recommend speciﬁc parameters for the survey:choice ofﬁeld,choice ofﬁlters,and depth needed for a meaningful advance.As with the original HDF,our purpose was to provide a public database using Director’s Discre-tionary Time on the Hubble Space Telescope for community use.This paper emphasizes the pa-rameters of the database rather than the subse-quent analysis,but it provides aﬁrst-order anal-ysis of the data to assess changes in the galaxy populations from the highest observable redshifts until the present.Thus,we assembled a team at the Space Tele-scope Science Institute to create the deepest visual-band image of the universe to date and put the observations in the public domain for commu-nity analysis.Like the HDF,this is a multi-color, pencil beam survey in a single ACSﬁeld.We call the resulting multi-color image the Hubble Ultra Deep Field(HUDF).2.Observations2.1.Field selectionTheﬁeld choice derived from a desire to min-imize the celestial foreground radiation,maxi-mize the accessibility to other astronomical ob-servatories,maximize the overlap with extant or planned deep observations at x-ray,infrared,and radio wavelengths,and maximize the observing eﬃciency of Hubble.The original HDF was lo-cated in Hubble’s continuous viewing zone(CVZ) to allow uninterrupted observations over a long period.The background light in CVZ orbits is often bright when observing in the part of the or-bit grazing the bright earth limb.The HDF over-came this limitation by taking images in the ul-travioletﬁlter,F300W,during the bright periods, because WFPC2images in thisﬁlter are detec-tor noise limited and relatively unaﬀected by in-creased background.The Wide Field Camera of ACS is not sensitive at ultraviolet wavelengths, and the enhanced background of the bright CVZ orbits would seriously limit their usefulness.We, therefore,decided not to require that the target ﬁeld be located in the CVZ,since it would not enhance the eﬃciency of the observations. Zodiacal dust within approximately30◦of the ecliptic plane is bright for Hubble;it was desirable to locate theﬁeld as far from the ecliptic as pos-sible.Declinations north of35◦are inaccessible from all major southern hemisphere observatories, particularly the planned Atacama Large Millime-ter Array(ALMA),designed to be an important tool for observations of distant galaxies.Declina-tions south of-40◦are inaccessible from Hawaii and all observatories northward.At the outset, we concentrated onﬁelds between-40◦and+35◦declination and more than35◦from the ecliptic plane.Within this declination range,there are a few places with very low Galactic dust and substan-tial investments of observing time from other pro-grams.The most prominent was the Chandra Deep Field South(CDF-S),a large(15′×15′)ﬁeld located in the direction3h30m-28◦.Thisﬁeld has very low Galactic cirrus emission and atomic hydrogen column density(Schlegel,Finkbeiner, &Davis1998),it passes through the zenith at the major observatories in Chile(the VLT,CTIO, Gemini South,Magellan,and ALMA),and it is ac-cessible from as far north as the VLA site in New Mexico.Furthermore,the CDF-S already has a substantial investment in deep x-ray observations with Chandra and XMM,and there are existing ACS observations through the Great Observato-ries Origins Deep Survey(GOODS,Giavalisco et al.2004)allowing some useful comparisons for the HUDF.There are also deep infrared observations with the Spitzer Space Telescope(Dickinson et al. 2004)CDF-S is larger than a single ACSﬁeld;sev-eral additional criteria guided the exact choice of pointing within it.The x-ray sensitivity with Chandra varies across theﬁeld,and it was de-sirable for the HUDF to coincide with a region of good x-ray sensitivity.There are several in-teresting objects identiﬁed through GOODS that deep observations would be most useful for,specif-ically a galaxy at redshift5.8and an old super-nova.We centered theﬁeld such that the high red-shift galaxy and old supernova were both covered, and the x-ray sensitivity was also very good.This choice produced aﬁeld centered on:RA(J2000) =3h32m39s,Dec(J2000)=-27◦47′29′′.1.Table1 lists the major characteristics of thisﬁeld.2.2.FiltersTheﬁlter choice was identical to that chosen by the GOODS team.This choice provides enough color information for rudimentary classiﬁcation of objects and enough wavelength coverage to search for the highest redshift galaxies.It also makes pos-sible an easy comparison of samples derived from both surveys.To detect objects at the highest possible redshifts,the observations needed to in-clude the longest wavelengthﬁlter,F850LP(z850), a band that was suﬃciently insensitive in WFPC2 (F814W)to limit its use for the HDF.The adja-cent F775W(i775)ﬁlter gives minimal overlap but contiguous wavelength coverage.Together,these two bands provide excellent sensitivity to the high-est redshift objects detectable with ACS,the i775-dropout sources,and are mandatory to search for objects at redshifts approaching7.Four bands are desirable to provide crude spec-troscopic analysis of the objects.Since the long-wavelength observations are background-limited, additional sensitivity could be gained by adding images at shorter wavelengths without loss of signal-to-noise ratio.The V606ﬁlter,F606W,is immediately adjacent to i775,broad,and provides excellent sensitivity to all objects at redshifts less than about4.The HDF incorporated an ultravioletﬁlter use-ful for identifying dropout sources at redshifts near 3.The ACS wideﬁeld camera is optimized for red wavelengths,making ultraviolet observations relatively insensitive.Since a primary goal was to identify samples at higher redshifts than the HDF, we chose the bluestﬁlter to be the B435band, F435W,immediately adjacent to V606band.Fol-lowing the conventions of the GOODS team,the bands are hereafter called B435,V606,i775,and z850.There are two other advantages to using the sameﬁlter set as GOODS.The overlap between the GOODS CDF-Sﬁeld and the HUDF makes it possible to compare objects directly in both sur-veys to calibrate completeness estimates for the shallower survey.Furthermore,science analyses can be carried out on the two data sets using iden-tical methods and minimizing systematic diﬀer-ences.Figure1plots the total detection eﬃciency for the four bands used for the observations.Theﬁg-ure includes the spectrum of a model galaxy at a redshift of5.8for comparison.Figure1shows that this very high redshift galaxy produces a sharp drop inﬂux between z850and i775with noﬂux at all in the shorter wavelength bands.The rela-tive detection eﬃciency also indicates the need for longer exposures in the longest wavelength bands to detect objects whose spectra are eitherﬂat or blue,typical of star forming galaxies at high red-shift.4000500060007000800090001000011000Wavelength Å0.20.40.60.81Transmission,FΝB435V606i775z850100Myr CSFz 5.8Fig. 1.—Theﬁlter transmission curves for the four bands used in this survey(colored lines)along with the spectrum of a model star forming galaxy at z=5.8(black).The spectrum is from the model of Bruzual&Charlot(2003)for a0.4so-lar metallicity galaxy undergoing continuous star formation for100Myr using the intergalactic ab-sorption curves of Madau(1995).2.3.DepthThere are several ways to estimate the depth needed to address the diﬀerent problems described in the introduction.However,we caution at the outset that so little is known about objects at the highest redshifts of interest that a conserva-tive approach would require depths well beyond those possible even with Hubble.We recognized at the outset that our goal was to obtain as deep an observation as possible with the amount of discretionary time available to the Director,and the depth would be constrained by the available pool.The resulting sensitivity is,nevertheless, well-suited to make progress on each issue.We adopt the concordance cosmology,ΩΛ=0.73,ΩM=0.27,h=0.71,throughout this paper for all analyses.The primary goal was to detect a statistically signiﬁcant sample of galaxies at redshifts between5and7.We set this goal at about100objects.Two additional goals are to study the luminos-ity function of high redshift galaxies at the faintend down to∼0.1L∗,and to observe low surface brightness features in galaxies that are missed inshallower surveys such as GOODS and the HDF,both of which will be aided by the faintest lim-iting magnitude that can be achieved by Hubble. The following paragraphs estimate what might be achieved with a limiting AB magnitude of∼29m, say.Assuming galaxy luminosity distributions are described by a Schechter function,it is possible to estimate the number of galaxies accessible to observation in any volume element of the uni-verse.SAGDP99determined a characteristic ap-parent magnitude at redshift3,m∗(3),of24.5(B-band)in the rest frame ultraviolet,correspond-ing to M∗=−20.8corrected to the assumed cos-mology;the local value is−20.2(Schechter1976.) Assuming M∗=−20.2,φ∗=0.016Mpc−3,and α=−1.6,the number of galaxies detected as a function of redshift per unit redshift in a single ﬁeld of∆Ωsr(11arcmin2for ACS)is:dNdz ∞x(z)φ∗Lαe−L dL,(1) where dV(1+z)10(M∗+k b(z)−m lim)/2.5,(2)with the luminosity distance,D L,in units of10pc and k b(z)the k-correction at redshift,z.These equations may be evaluated numerically;the re-sults are given in Table2for an assumed magni-tude limit between28and29.We also calculated the expected number of objects appearing in the V606,i775,and z850bands assuming all objects had the spectrum of a source undergoing continuous star formation for100Myr(Bruzual and Charlot 2003)and accounting for intergalactic hydrogen absorption(Madau1995)to illustrate where the objects drop out of eachﬁlter.The numbers in Table2are certainly much larger than a real survey would see.We have notattempted to correct for many observational ef-fects that would preclude galaxy detection in asurvey or for the expected mixture of source sizes,types,colors,etc.Furthermore,the density,φ∗, of distant populations appears to be several timessmaller than the local value used in these calcu-lations(SAGDP99.)The point of this estimate is to show that the expected number of sources is so large that even a few percent detection probability would yield statistically useful samples of galaxies.It is evident from Table2that even a detectionlimit of28m in z850would easily satisfy the goal of detecting∼100objects above redshift5.It would also reach below L∗at redshifts approach-ing7.There are several large uncertainties that could change these numbers in either direction:if L∗continues to increase beyond redshift3(e.g. Gabasch et al.2004a,b),there will be more faint objects to increase the counts and move further into the faint end of the luminosity function;how-ever,ifφ∗decreases owing either to a smaller num-ber density of galaxies in the early universe or cos-mic error,the number of detected galaxies will decrease.The two eﬀects oﬀset one another for number counts and introduce a diﬃculty of inter-pretation without a well-characterized luminosity function.A z850band limiting magnitude of28requires oforder one hundred orbits of dedicated Hubble ob-servations.The maximum available was400,and those needed to be divided among the four bands to give adequate spectral information.We chose to allocate144orbits each to the z850and i775 bands with estimated limiting magnitudes of28.7 and29.2,respectively.The remaining112orbits were split equally between B435and V606,whose estimated limiting magnitudes were then29.1and 29.3.With these sensitivities,the HUDF would, therefore,moveﬁrmly into the range needed to as-semble samples of high redshift galaxies and might even see substantial evolution in the properties of galaxies when compared with later epochs.2.4.Schedule andﬁeld orientationThe observations were scheduled for two peri-ods during which the roll angles could be con-trolled to produce a nearly square image.Schedul-ing400orbits at the same pointing and with con-strained orientations required the use of four roll angles in all:40◦,44◦,310◦,and314◦for the po-sition angle of the+U3axis on the sky to increase the target visibility and facilitate scheduling.Ta-ble3lists the schedule of observations in orbits for eachﬁlter.Each observation or visit consisted of two orbits with two exposures per orbit.The exposure time was typically1200seconds but in a few cases the exposures had to be shortened to850seconds.The total exposure time is just under1million seconds.2.5.Small Scale Pointing:DithersIn addition to the large rotations between dif-ferent phases of the observations that were re-quired for scheduling,smaller shifts in telescope pointing were applied to diﬀerent observations at the same position angle.These small changes in pointing between exposures,referred to as dithers, were introduced on two scales.First,small-scale dithers were applied to each of the four exposures within a two orbit visit. This dither pattern improved the sampling of theﬁnal image by introducing half-pixel oﬀ-sets.The ACS/WFC detector critically samples the point spread function(PSF)in the reddest bands but signiﬁcantly undersamples the PSF at shorter wavelengths.Such undersampling leads to loss of spatial information and aliasing artifacts. The introduction of sub-pixel dithering improves the sampling and allows the reconstruction of a higher-resolutionﬁnal image and a reduction of artifacts.In the case of ACS/WFC,half-pixel dithers or small integer numbers of pixels plus a half-pixel in both X and Y directions provide adequate sam-pling.The integer pixel components of the dither-ing were chosen to create the most compact dither pattern that ensured that a bad row or column could not overlap in the combined image because the pointings were always at least1.5pixels away from others in both X and Y.Thisﬁnal four-point dither,suggested by Stefano Casertano,is given in Table4.The most compact pattern was chosen because the exact sub-pixel shifts will be diﬀerent far from the center of the detectors owing to the very large non-linear component of the ACS/WFC optical distortion.The dither pattern minimizes this eﬀect and ensures good sampling across the ﬁeld.Additional dithers of approximately3and6 arcseconds in length in the direction perpendic-ular to the gap between the two ACS/WFC chips were introduced between visits.These oﬀsets en-sure that the regions of sky falling in the gap be-tween the two ACS/WFC chips had at least two thirds of the exposure of the rest of theﬁeld and hence minimized the lack of uniformity of theﬁnal exposure map.3.Data analysis3.1.Basic data reductionEach of the ACS/WFC exposures was pro-cessed through the standard ACS data pipeline, CALACS.Theﬁrst step removed the bias level, subtracted the dark current,corrected theﬂatﬁeld and gain variations,eliminated known bad pixels, and calculated the photometric zeropoint.To achieve optimal calibration,several refer-enceﬁles were created speciﬁcally for these ob-servations:improved dark current correctionﬁles (hyperdarks),improvedﬂatﬁelds,and bad pixel ﬁles.The hyperdarks were created using all the dark-current frames from the6-month period encom-passing the HUDF observations.Theseﬁles pro-vide higher signal-to-noise ratios than the typi-cal dark referenceﬁles that are subtracted during standard calibration and provide a more accurate representation of the overall dark current struc-ture appropriate to the HUDF exposures.Newﬂatﬁeld images for eachﬁlter were pro-duced by applying aﬂatﬁeld technique that cor-rects only low spatial-frequency variations based on stellar photometry of47Tucanae.These new ﬂatﬁeld images(L-ﬂats)produced a more uni-form sky level across the images than the stan-dard pipeline products.After re-calibrating the data with these L-ﬂats,the images had residual ﬂux of order2%of the sky level that we ascribe to scattered light from bright sources outside the ﬁeld of view.We produced images of these residu-als from the re-calibrated images and subsequently removed the scattered light by the following pro-cedure:1.All exposures from the pipeline were com-bined to create an image of theﬁeld.。

科技英语第十九课翻译

Lesson 19NASA Missions-the Space Science Enterprises Ahead1 In the decade ahead we have the opportunity to address many of these exciting and engaging issues, developing missions to gain new Answers and enrich the story.在未来的十年里,我们有机会去从事这些令人激动和迷人的领域,发展任务去增加答案和丰富阅历.There will be twists and turns along the way, unexpected discoveries that will show us the Universe is not quite the way wo thought.这个过程会很坎坷,意外地发现会让我们知道这个宇宙不是我们想的那样.And there will almost certainly be difficulties .并且几乎都是困难.Developing new tools to expend the frontiers of the known is always challenging.发展新的工具会扩大已知的前沿,总是很有挑战性的.But a coherent, practical, and affordable strategy is feasible. 但是一个相关性的,实用性的,负担得起的战略可行.NASA's Space Science Enterprise can provide more precise answers to Fundamental questions about the formation and evolution of the Universe,美国国家航空航天局的太空科学局可以提供更多的精确的回答关于太空的形成和演变的基本问题:how the Sun influences Earth, the history of planets and satellites in our Solar system, and the occurrence of life either in our tiny region of space or in the larger neighborhood of our Galaxy.太阳怎样影响地球,在太阳系里的行星和卫星历史,还有在生活中无论是微小地区或者更大的银河系的附近一带所发生的事.The Program: 2000-2004项目:2000-20042 Missions and programs expected to start or be enhanced in 2000-任务和项目都期盼在2000~20004年开始或提高科学目标局的2004 will contribute to achieving the Enterprise Science Goals. 贡献.GOAL 1-Understand how structure in our Universe(e.s.clusters of galaxies) emerged from the Big Bang.目标1、明白宇宙大爆炸是怎么样形成的。

The Metallicity of High Redshift Galaxies The Abundance of Zinc in 34 Damped Lyman Alpha Sy

a rXiv:as tr o-ph/97412v111Apr1997THE METALLICITY OF HIGH REDSHIFT GALAXIES:THE ABUNDANCE OF ZINC IN 34DAMPED LYMAN αSYSTEMS FROM z =0.7TO 3.4Max Pettini Royal Greenwich Observatory,Madingley Road,Cambridge,CB30EZ,UK e-mail:pettini@ Linda J.Smith Department of Physics and Astronomy,University College London,Gower Street,London WC1E 6BT,UK e-mail:ljs@ David L.King Royal Greenwich Observatory,Madingley Road,Cambridge,CB30EZ,UK e-mail:king@ Richard W.Hunstead School of Physics,University of Sydney,NSW 2006,Australiae-mail:rwh@.auABSTRACTWe report new observations of Zn II and Cr II absorption lines in10dampedLymanαsystems(DLAs),mostly at redshift z abs>∼2.5.By combining these results with those from our earlier survey(Pettini et al.1994)and other recent data,weconstruct a sample of34measurements(or upper limits)of the Zn abundance relativeto hydrogen[Zn/H];the sample includes more than one third of the total number ofDLAs known.The plot of the abundance of Zn as a function of redshift reinforces the two mainﬁndings of our previous study.(1)Damped Lymanαsystems are mostly metal-poor,at all redshifts sampled;the column density weighted mean for the whole data setis[Zn/H]=−1.13±0.38(on a logarithmic scale),or approximately1/13of solar.(2)There is a large spread,by up to two orders of magnitude,in the metallicities wemeasure at essentially the same redshifts.We propose that damped Lymanαsystemsare drawn from a varied population of galaxies of diﬀerent morphological types andat diﬀerent stages of chemical evolution,supporting the idea of a protracted epoch ofgalaxy formation.At redshifts z>∼2the typical metallicity of the damped Lymanαsystems is in agreement with expectations based on the consumption of H I gas implied by the recentmeasurements ofΩDLA by Storrie-Lombardi et al.(1996a),and with the metal ejectionrates in the universe at these epochs deduced by Madau(1996)from the ultravioletluminosities of high redshift galaxies revealed by deep imaging surveys.There areindications in our data for an increase in the mean metallicity of the damped Lymanαsystems from z>3to≈2,consistent with the rise in the comoving star formationrate indicated by the relative numbers of U and B drop-outs in the Hubble Deep Field.Although such comparisons are still tentative,it appears that these diﬀerent avenuesfor exploring the early evolution of galaxies give a broadly consistent picture.At redshifts z<1.5DLAs evidently do not exhibit the higher abundances expected from a simple closed-box model of global chemical evolution,although the number of measurements is still very small.We speculate that this may be due to an increasing contribution of low surface brightness galaxies to the cross-section for damped Lymanαabsorption and to the increasing dust bias with decreasing redshift proposed by Fall and collaborators.However,more DLAs at intermediate redshifts need to be identiﬁed before the importance of these eﬀects can be assessed quantitatively.The present sample is suﬃciently large for aﬁrst attempt at constructing the metallicity distribution of damped Lymanαsystems and comparing it with thoseof diﬀerent stellar populations of the Milky Way.The DLA abundance histogramis both broader and peaks at lower metallicities that those of either thin or thick disk stars.At the time when our Galaxy’s metal enrichment was at levels typical of DLAs,its kinematics were closer to those of the halo and bulge than a rotationally supported disk.Thisﬁnding is at odds with the proposal that most DLAs are large disks with rotation velocities in excess of200km s−1,based on the asymmetric proﬁles of absorption lines recorded at high spectral resolution.Observations of the familiar optical emission lines from H II regions,which are within reach of near-infrared spectrographs on8-10m telescopes,may help resolve this discrepancy.Subject headings:cosmology:observations—galaxies:abundances—galaxies: evolution—quasars:absorption lines1.INTRODUCTIONIn the last twelve months there has been a dramatic increase in our ability to identify normal galaxies at z≃3,study their stellar populations,and measure the rates of star formation and metal production in the universe over most of the Hubble time(Steidel et al.1996;Madau et al.1996).The most prominent features in the spectra ofﬁeld galaxies at high-redshift(as is the case in the ultraviolet spectra of nearby star-forming galaxies)are strong interstellar lines which are similar,both qualitatively(in the range of ionization stages seen)and quantitatively(in the strengths of the absorption),to those in damped Lymanαsystems;this similarity is consistent with the view that this class of QSO absorbers traces the material available for star formation at z>∼2(e.g.Wolfe1995).The connection between normal galaxies and damped Lymanαsystems (DLAs)is a particularly important one to make and clarifying several aspects of this connection remains a priority.The reason is simple:QSOs with known DLAs are typically more than5 magnitudes brighter than a L∗galaxy at the same redshift.Consequently,we will inevitably continue to rely mostly on QSO absorption line spectroscopy for the study of physical conditions in the early stages of galaxy formation.Since1990(Pettini,Boksenberg,&Hunstead1990)we have been conducting a survey of metallicity and dust in DLAs taking advantage of the diagnostic value of weak transitions of Zn II and Cr II.As explained in that paper(see also the critical reappraisal of the technique in Pettini et al.1997),[Zn/H]1is a straightforward measure of the degree of metal enrichment analogous to the stellar[Fe/H],while[Cr/Zn]reﬂects the extent to which grain constituents are removed from the gas phase and thereby gives an indication of the dust-to-metals ratio.The major results of the survey were reported in Pettini et al.(1994).From the analysis of Zn and Cr abundances in17 DLAs,mostly at z≃2,we concluded that the typical metallicity of the universe at a look-back time of∼13Gyr(H0=50km s−1Mpc−1;q0=0.01)was Z DLA=1/10Z⊙.We further foundthat there is a considerable range—by up to two orders of magnitude—in the degree of metal enrichment reached by diﬀerent damped Lymanαgalaxies at essentially the same epoch,and that even at these early stages of galaxy formation dust appears to be an important component of the interstellar medium,leading to the selective depletion of refractory elements from the gas.A natural next step is to extend the Zn and Cr abundance measurements over a wider range of redshifts than that considered by Pettini et al.(1994)with the ultimate aim of identifying the emergence of heavy elements and dust in galaxies and following their build-up with time.To this end we have continued our survey since1994;the full sample now consists of34DLAs,more than one third of the total number known(Wolfe et al.1995).In this paper we present the new data and consider the conclusions that can drawn from the whole set of measurements of[Zn/H]; preliminary reports have appeared in conference proceedings(e.g.Pettini et al.1995a;Smith et al.1996).Ourﬁndings on the abundance of dust from consideration of the[Cr/Zn]ratio in the same sample have been reported separately(Pettini et al.1997).Recently,Lu et al.(1996)have addressed similar questions from measurements of[Fe/H]in20DLAs using high-resolution echelle spectra acquired with the Keck telescope.These authors reach conclusions which are in agreement with those presented here regarding the emergence of heavy elements at high redshifts,although the analysis of[Fe/H]is complicated by the fact that this ratio,unlike[Zn/H],depends on both the metallicity and dust content of the interstellar medium.Before proceeding it is useful to point out that in cases where DLAs from the present sample have been reobserved with HIRES on Keck(Wolfe et al.1994;Wolfe1995;Prochaska&Wolfe 1997a),[Zn/H]has been found to be in good agreement with the values measured in our survey, which is based on4-m telescope data(see§2below).While the exceptional quality of the Keck observations has made possible several new aspects of this work,including the study of the relative abundances of a wide range of elements and the analysis of the kinematics of the absorbing gas, the basic survey of metallicity in DLAs can be carried out satisfactorily with4-m class telescopes.The main reason for this is the optically thin nature of the Zn II and Cr II lines in most DLAs proposed by Pettini et al.(1990)and conﬁrmed by subsequent Keck spectra.2.OBSER V ATIONS AND DATA REDUCTIONThe new data reported in this paper consist of observations of10DLAs in9QSOs obtained between March1994and February1996(an additional candidate DLA from the low dispersion survey by Storrie-Lombardi et al.(1996b)—at z abs=3.259in the z em=4.147BAL QSO 1144−073—was shown not to be a damped system by our higher resolution observations of the Lymanαabsorption line).In Table1we have collected relevant information for the10DLAs; the references listed in column(4)are the papers where the damped nature of the absorber was ﬁrst identiﬁed.The absorption redshifts measured from associated metal lines in our blue and red spectra are listed in column(5);with6new DLAs at z abs>2.5,we have tripled the number of absorbers in this redshift regime compared with our earlier sample.The observations,reduction of the spectra and derivation of Zn and Cr abundances followed the procedures described in Pettini et al.(1994)and the interested reader is referred to that paper for a detailed treatment.Brieﬂy,the observations were carried out mostly with the double-beam cassegrain spectrograph of the William Herschel telescope on La Palma,Canary Islands;additional red spectra were secured with the cassegrain spectrograph of the Anglo-Australian telescopeat Siding Spring Observatory,Australia.At z abs>2.5the Zn IIλλ2025.483,2062.005andCr IIλλ2055.596,2061.575,2065.501multiplets are redshifted longwards of7175˚A,where the quantum eﬃciency of CCDs falls with increasing ing EEV and Tektronix CCDs we generally found it necessary to integrate for longer than∼20000s(column8of Table1)in order to achieve S/N between9and46(column9).With a spectral resolution of0.75–1.1˚A FWHM(column7),the corresponding3σdetection limits for the rest frame equivalent widthsof unresolved Zn II and Cr II absorption lines range from W0(3σ)=66to14m˚A(column10). Theﬁnal“depth”of the survey—that is the lowest metallicity that can be measured—depends on the combination of W0(3σ)and the neutral hydrogen column density N(H0).Since the values of N(H0)in the new DLAs observed span one order of magnitude(see§3below),it is the sight-lines with the largest column densities of gas which provide the most stringent limits on metal abundances.Accordingly,we have tended to select DLAs for the present survey primarily on the basis of the value of N(H0).In Figure1we have reproduced portions of the QSO spectra encompassing the regions where the Zn II and Cr II lines are expected in the10DLAs in Table1.As can be seen from theﬁgure, the absorption lines sought are detected in approximately half of the cases.Table2lists redshifts and rest-frame equivalent widths for the detections;in the other cases the3σlimits given in column(10)of Table1apply.With the double-beam spectrograph on the WHT we were able to record portions of the blue spectrum of each QSO,centred on the damped Lymanαline,simultaneously with the red arm observations aimed at the Zn II and Cr II lines.The blue detector was either the Image Photon Counting System or a thinned Tektronix CCD;exposure times were the same as those given in column(8)of Table1.A600grooves/mm grating was used to record a800˚A wide interval of the spectrum with a resolution of∼1.5˚A FWHM.This conﬁguration was chosen in preference to the higher resolving power achievable with a1200grooves/mm grating because a good deﬁnition of the QSO continuum is a key factor in determining the accuracy with which N(H0)can be deduced from the proﬁle of the damping wings of the Lymanαabsorption line.Normalised portions of the blue spectra are shown in Figure2together with ourﬁts to the damped Lymanαlines.The theoretical damping proﬁles are centred at the redshifts of the O Iλ1302.1685lines which are encompassed by our blue data.3.ZINC AND CHROMIUM ABUNDANCESThe main results of our survey are collected in Table3which includes the10DLAs in Table 1and7additional systems for which data have been published since our earlier study(Pettini et al.1994).Values of the neutral hydrogen column density N(H0)are listed in column(3)of Table 4;the typical accuracy of these measurements,including the uncertainty in the placement of the continuum,is±20%.N(H0)is likely to account for most of the neutral gas in each DLA given the low molecular fractions which apply to these absorbers at high redshifts(Levshakov et al.1992; Ge&Bechtold et al.1997;´Cirkovi´c et al.1997).Columns(3)and(6)of Table3give the column densities of Zn+and Cr+respectively, deduced from the measured equivalent widths(or upper limits)assuming no line saturation. That this is generally the case is indicated by:(1)the weakness of the absorption lines;(2)the equivalent width ratios of lines within each multiplet which,when measurable,are usually close to the ratios of the corresponding f-values(Bergeson&Lawler1993);and(3)the resolved absorption proﬁles recorded with HIRES on Keck for many DLA systems,including some in common with the present survey(Lu et al.1996;Prochaska&Wolfe1997a).There are of course exceptions,such as the z abs=2.5842system in Q1209+093—see the discussion at§3.12below.The important point, however,is that it is usually possible with the signal-to-noise ratio and resolution of our data to assess the degree of saturation of the Zn II and Cr II lines.Column(4)lists the ratios N(Zn+)/N(H0)derived by dividing the entries in column(3)by those in column(3)of Table4;comparison with the solar abundance of Zn,log(Zn/H)⊙=−7.35 (Anders&Grevesse1989),then leads to underabundances of Zn by the factors given in column (5).The corresponding values for Cr(log(Cr/H)⊙=−6.32)are given in column(8)and column (9)lists the ratio N(Cr+)/N(Zn+)in cases where it could be determined.In taking the ratios N(Zn+)/N(H0)and N(Cr+)/N(H0)as measures of(Zn/H)and(Cr/H),we implicitly assume that there is little contribution to the observed Zn II and Cr II absorption from ionised gas(which would not produce Lymanαabsorption).This is likely to be the case given the large column densities of H I,and indeed there are no indications to the contrary in our data.In particular,we found no signiﬁcant diﬀerences in redshift between the Zn II and Cr II lines,when detected,and O Iλ1302.1685which arises only in H I regions.Should this assumption be shown to be incorrect,however,the values of[Zn/H]and[Cr/H]deduced here would then be upper limits to the true abundances.We now comment brieﬂy on each DLA in Table3.3.1.Q0000−263;z abs=3.3901Our observations of this DLA,the highest redshift absorber in the survey,have been described in Pettini et al.(1995a).While Zn IIλ2025.483remains undetected,despite the sensitive limit reached in a total exposure time of58200s,we do record weak Cr II absorptions at the4σ(λ2055.596)and3σ(λ2061.575)signiﬁcance levels.Cr IIλ2055.596is expected to be stronger than Zn IIλ2025.483if the fraction of Cr locked up in dust grains is less than about50%.With N(H0)=(2.5±0.5)×1021cm−2(Savaglio,D’Odorico,&Moller1994),this is one of the highest column density systems in our sample.We conclude that the abundance of Zn is less than1/80of the solar value;this estimate is∼5times more sensitive than the previous limit(Savaglio et al. 1994).The abundance of Cr,[Cr/H]≃−2.2±0.1,is similar to those of other elements measured by Molaro et al.(1996)and Lu et al.(1996),making this DLA one of the most metal-poor in our sample.3.2.Q0056+014;z abs=2.7771This QSO is from the Large Bright Quasar Survey by Chaﬀee et al.(1991).We deduceN(H0)=(1.3±0.2)×1021cm−2fromﬁtting the core of the damped Lymanαline,in reasonable agreement with the value log N(H I)=21.0reported by Wolfe et al.(1995).As can be seen from Figure1,the Zn II and Cr II absorption lines are broad and shallow in this DLA,spanning≈200km s−1.The stronger member of the Zn II doublet,λ2025.483, falls within the atmospheric A band.Plotting the four absorption lines labelled in Figure1on the same velocity scale suggests that most of feature“1”is not due to Zn IIλ2025.483,but rather to poorly corrected telluric absorption.From the equivalent widths of Cr IIλ2055.596 andλ2065.501(features2and4in Figure1),which are consistent with the optically thin ratio of2:1,we deduce a weighted mean N(Cr+)=(2.8±0.4)×1013cm−2.This column density of Cr+produces an equivalent width W0=(82±12)m˚A for Cr IIλ2061.575;since we measure W0=(117±16)m˚A for feature3,which is a blend of Cr IIλ2061.575and Zn IIλ2062.005,we conclude that W0=(35±20)m˚A for the latter.This in turn corresponds to N(Zn+)= (3.5±2)×1012cm−2.Thus both Zn and Cr appear to be≈20times less abundant than in the Sun.Our red spectrum also shows several Fe II lines from an absorption system at z abs=2.3044, including:Fe IIλ2344.214(visible in Figure1atλobs=7748.46˚A)with W0=(470±12)m˚A; Fe IIλ2367.5905with W0=(64±6)m˚A;Fe IIλ2374.4612with W0=(220±14)m˚A;andFe IIλ2382.765with W0=(640±12)m˚A.3.3.Q0201+365;z abs=2.462Keck observations of this DLA have been published recently by Prochaska&Wolfe(1996) who deduced relatively high abundances of Zn and Cr,respectively∼1/2and∼1/8of solar. Evidently,even at redshifts as high as2.5some galaxies had already undergone signiﬁcant chemical evolution and enriched their interstellar media in heavy elements to levels comparable with that of the Milky Way today.3.4.Q0302−223;z abs=1.0093Lanzetta,Wolfe,&Turnshek(1995)proposed this as a candidate DLA system on the basis of low-resolution IUE data;a subsequent UV spectrum secured with the Faint Object Spectrograph on the Hubble Space Telescope conﬁrmed that N(H0)=(2.15±0.35)×1020cm−2(Pettini&Bowen 1997).Recent WHT observations of Zn II and Cr II lines by Pettini&Bowen(1997)have shown the abundances to be1/3and1/8of solar respectively.After subtraction of the QSO radial proﬁle from HST WFPC2images of theﬁeld,Le Brun et al.(1997)identiﬁed two galaxies which may be producing the absorption;at z=1.009they would have luminosities L≈0.2L∗and≈L∗and distances of12and27h−150kpc respectively from the QSO sight-line.3.5.Q0454+039;z abs=0.8596The abundances of Zn and Cr reported by Steidel et al.(1995a)correspond to[Zn/H]=−0.83±0.08and[Cr/H]=−1.01±0.05if the experimentally measured f-values of the Zn II and Cr II multiplets(Bergeson&Lawler1993)are adopted for consistency with the rest of the present study.Deep images of the QSOﬁeld both from the ground(Steidel et al.1995a)and with HST(Le Brun et al.1997)suggest that the absorber is a compact galaxy with L≈0.25L∗(q0=0.05) at a projected distance of8h−150kpc from the QSO.3.6.Q0836+113;z abs=2.4651This is the faintest QSO in our survey(Hunstead,Pettini,&Fletcher1990)and the S/N of the red spectrum remains modest despite the considerable investment in exposure time(Table 1).Combined with the relatively low H I column density of(3.8±0.4)×1020cm−2,the3σupper limits to the Zn II and Cr II lines place limits on the abundances of Zn and Cr which are less stringent than in most other DLAs considered:[Zn/H]≤−0.8and[Cr/H]≤−1.2.The blue spectrum shown in Figure2was recorded with the IPCS on the WHT in March1994.Note that,of all the damped Lymanαlines reproduced in Figure2,this isthe only instance where there appears to be weak emission in the core of the absorption line.The lineﬂux,(2±0.7)×10−17erg s−1cm−2,agrees within the errors with the value of (2.9±0.7)×10−17erg s−1cm−2reported by Hunstead et al.(1990)from independent data obtained in April1987with a diﬀerent IPCS detector on the AAT.The two sets of observations were obtained with the same slit width(1.2arcsec)and at the same position angle on the sky(150 degrees).3.7.Q0841+129;z abs=2.3745,2.4764The spectrum of this bright(V≃17),high redshift(z≃2.5,estimated from the onset of the Lymanαforest)BL Lac object discovered by C.Hazard(private communication)shows two DLAs(see Figure2),making it a highly suitable target for follow-up high resolution observations.As can be seen from Figure1,in the lower redshift system we detect features2and3;the strength of the latter indicates a signiﬁcant contribution from Zn IIλ2062.005to the blend. Following a procedure similar to that described for Q0056+014at§3.1above,we deduce N(Cr+) =(9.5±2)×1012cm−2from the equivalent widths of Cr IIλ2055.596andλ2065.501.This in turn leads us to estimate that approximately half of the equivalent width of feature3is due to Zn IIλ2062.005with W0=(24±9)m˚A.Together with the3σupper limit W0(2025)≤26m˚A for the stronger member of the doublet,this then implies N(Zn+)=(1.8±0.5)×1012cm−2.Thus weﬁnd that Zn and Cr at z abs=2.3745are underabundant by factors of23and45 respectively,relative to solar values.Similar,or lower,abundances apply to the z abs=2.4764 DLA,given the lack of detectable Zn II and Cr II lines(see Table3).3.8.Q0913+072;z abs=2.6183The signal-to-noise ratios of our spectra of this bright QSO are among the highest in the survey—see Table1and Figures1and2.The column density of neutral hydrogen is however comparatively low,N(H0)=(2.3±0.4)×1020cm−2.The lack of Zn II and Cr II absorption even at S/N=46implies underabundances by factors of more than14and32respectively.3.9.Q0935+417;z abs=1.3726Lanzetta et al.(1995)estimated N(H0)≃2×1020cm−2for this candidate DLAfrom low resolution IUE data;a subsequent HST FOS spectrum conﬁrmed that N(H0)= (2.5±0.5)×1020cm−2(Lanzetta&Meyer1996,private communication).With this value of the hydrogen column density,the observations by Meyer,Lanzetta,&Wolfe(1995)imply[Zn/H]=−0.80and[Cr/H]=−0.90.3.10.Q1104−180;z abs=1.6616Smette et al.(1995)identiﬁed this DLA in the spectrum of the brighter(B=16.7)component of this gravitationally lensed QSO pair.From AAT observations obtained with an instrumental setup similar to that used in our survey,these authors estimated N(H0)=6×1020cm−2. They also reported detections of Zn II and Cr II absorption lines with equivalent widthsW0(2025.483)=(75±20)m˚A and W0(2055.596)=(57±20)m˚A respectively.If the lines are unsaturated[Zn/H]=−0.80and[Cr/H]=−1.30.3.11.Q1151+068;z abs=1.7736Even though the damped Lymanαline falls in the crowded near-UV spectrum of thisz em=2.762QSO(see Figure2),our estimate N(H0)=(2.0±0.5)×1021cm−2is in very good agreement with log N(H I)=21.3published by Turnshek et al.(1989).The ratios of equivalent widths within the Zn II and Cr II multiplets strongly suggest that the lines are optically thin;Zn and Cr are both underabundant by a factor≈40.Our red spectrum,which covers the region5500−5900˚A,shows three C IVλλ1548,1550 doublets at z abs=2.5629,2.7069and2.7551respectively.3.12.Q1209+093;z abs=2.5843This is another high column density DLA;we measure N(H0)=(2.0±0.5)×1021cm−2 which compares well with log N(H I)=21.4reported by Lu et al.(1993).The Zn II and Cr IIlines are the strongest encountered in the entire survey of34DLAs(see Table2).Fitting the√absorption proﬁles requires b=50km s−1(as usual,b=still suﬃcient to establish that the abundances of Zn and Cr are less than1/10and1/23of solar respectively.3.15.Q1946+769;z abs=2.8443This z em=3.051QSO,intrinsically one of the most luminous known,is suﬃciently bright to have been studied extensively at echelle resolutions and high S/N with4-m telescopes(Fan& Tytler1994;Lu et al.1995;Tripp,Lu,&Savage1996).However,the hydrogen column density in the z abs=2.8443DLA is relatively low,N(H0)=(2±0.5)×1020cm−2(Lu et al.).Consequently, the upper limits[Zn/H]≤−0.82and[Cr/H]≤−1.00deduced by these authors are rather uninformative given that the true metallicity is∼30times lower([Fe/H]=−2.44±0.13).3.16.Q2239−386;z abs=3.2810This QSO is faint and the absorber is at high redshift;the combination of these two factors resulted in the longest integration time in the survey(see Table1).AdoptingN(H0)=5.8×1020cm−2measured by Lu&Wolfe(1994),we deduce Zn and Cr underabundances by factors of more than11and13respectively.The Cr measurement is based on the weakest member of the triplet,Cr IIλ2065.501;λ2061.575is aﬀected by a strong sky emission line andλ2055.596,which at z abs=3.2810is redshifted toλobs=8802.82˚A,falls very close to Mn IIλ2606.462at z abs=2.3777,the redshift of a second DLA along this line of sight(Lu&Wolfe1994).Based on the strengths of the other two members of the Mn II triplet,λ2576.877atλobs=8703.55˚A andλ2594.499atλobs=8763.97˚A, the feature labelled2in the last panel of Figure1is mostly Mn IIλ2606.462.The two strong absorption lines also visible in thisﬁgure are Fe IIλλ2586.6500,2600.1729at z abs=2.3777.4.DISCUSSIONOur total sample,which consists of measurements(or upper limits)of[Zn/H]in34DLAs over the redshift range z abs=0.6922−3.3901,is constructed by combining data for the17DLAs in Table3with those for the15DLAs in Table3of Pettini et al.(1994)and with the further addition of two DLAs in Q0528−250(Meyer et al.1989)which were included in the sample considered by Pettini et al.(1994)but not listed in their Table3.All the points in Figure3are based on the f-values of the Zn II doublet by Bergeson&Lawler(1993)and the meteoritic solar abundance of Zn from the compilation by Anders&Grevesse(1989)2.We now consider what implications can be drawn from this extensive survey on the chemical evolution of the neutral content of the universe and on the relationship of damped Lymanαsystems to present-day spiral galaxies.4.1.Chemical Evolution of Damped LymanαSystemsFigure3shows the abundance of Zn as a function of redshift.The enlarged sample conﬁrms the two main conclusions reached by Pettini et al.(1994):(1)Damped Lymanαsystems,at all redshifts probed,are generally metal-poor and presumably arise in galaxies at early stages of chemical evolution.(2)There appears to be a large range in the values of metallicity reached by diﬀerent galaxies at the same redshift,pointing to a protracted‘epoch of galaxy formation’and to the fact thatchemical enrichment probably proceeded at diﬀerent rates in diﬀerent DLA galaxies.While weﬁnd gas with near-solar metallicities at redshifts as high as z≃2.5,there are also examples of galaxies with abundances less than1/10solar at a time when the disk of the Milky Way diﬀered little from its present-day composition.At redshifts z≃2−2.5the full range of metal abundances spans about two orders of magnitude.Although for metallicities Z DLA<∼1/50Z⊙the Zn II lines become vanishingly small and only upper limits to the abundance of Zn can be deduced, we do know from echelle spectroscopy of more abundant astrophysical elements that values of Z DLA<∼1/100Z⊙are not uncommon at z abs=2−3(see Figure1of Pettini et al.1995a).These two results are considered quantitatively in Table5where in the last column we list, for various subsets of our sample,the column density-weighted mean abundance of Zn[ Zn/H DLA ]=log (Zn/H)DLA −log(Zn/H)⊙,(1) wheren i=1N(Zn+)i(Zn/H)DLA =。

Searches for galaxies at z 4 through Lyman-limit imaging

Colour–colour plots for the magnitude ranges in question are shown in Figure 1. Those for objects for which spectra are available are shown in Figure 2.
18000 2800 2400
12600 1800 1800 6600
7200 5400 2700 5400
Sensitivity limita
26.3 25.9 26.0 26.3 26.5 26.0 27.2 25.7 26.1 25.7
24.1 27.0 26.2 25.8
a 2.5σ limit in AB magnitudes for 1.5′′ radius aperture. In practice galaxies will be detected below these limits if they are suﬃciently compact for signiﬁcant excess ﬂux to be recorded in at least six contiguous pixels. b This narrow-band ﬁlter was a redshifted Hα ﬁlter with peak response at 656.5nm. This wavelength corresponds approximately to the wavelength of the Lyα line at the redshift of 6C 0140+326.
Abstract. We present preliminary results of a search for galaxies at z ∼> 4 through Lyman–limit imaging of the ﬁelds of known high–redshift radio–galaxies. Objects were selected by means of their broad–band colours, and spectroscopy of candidate objects in one of the ﬁelds has been performed through multi–slit spectroscopy at the 4.2m William Herschel Telescope. These spectra show some of the ﬁrst z > 4 galaxies to be identiﬁed using the Lyman break technique.

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天文望远镜礼物寄语英文1. "May this telescope help you explore the vastness of the Universe and uncover its mysteries. Enjoy your stargazing adventures!"2. "Wishing you many nights of clear skies and unforgettable celestial discoveries with your new telescope. Happy stargazing!"3. "May this telescope bring you closer to the stars and allow you to witness the beauty of the cosmos. Enjoy the magical journey of exploring the Universe!"4. "Here's to a lifetime of stargazing and awe-inspiring discoveries with your new telescope. Happy exploring!"5. "May each night you spend under the stars with your new telescope be filled with wonder, amazement, and new discoveries. Enjoy the beauty of the Universe!"6. "Wishing you endless hours of stargazing pleasure and countless unforgettable memories with your new telescope. Happy exploring!"7. "May this telescope open your eyes to the wonders of the Universe and ignite a lifelong passion for astronomy. Enjoy your cosmic adventures!"8. "As you embark on your stargazing adventures, may this telescope be your guide to exploring the mysteries of the Universe. Happy journeying!"9. "Here's to many nights of peaceful contemplation and profounddiscoveries with your new telescope. Enjoy the beauty and vastness of the cosmos!"10. "Wishing you clear skies, boundless curiosity, and magnificent celestial encounters with your new telescope. Happy stargazing!"11. "May your new telescope bring you closer to the beauty of the night sky and reveal the wonders that lie beyond. Enjoy your cosmic exploration!"12. "Here's to a gift that will take you on a journey through space and time. Wishing you endless fascination and discovery with your new telescope!"13. "May this telescope gift bring you closer to the secrets of the Universe and fill your nights with celestial marvels. Happy stargazing!"14. "Wishing you a celestial voyage filled with breathtaking sights and profound insights with your new telescope. Enjoy your cosmic journey!"15. "May your new telescope gift inspire you to reach for the stars, explore the unknown, and uncover the wonders of the universe. Happy exploring!"16. "Here's to the gift of discovering the magic that lies beyond our world. May your new telescope ignite a lifelong love affair with the stars. Enjoy your cosmic adventures!"17. "Wishing you countless nights of wandering among the stars, marvelling at the vastness of the Universe, and discovering the wondersthat it holds. Happy stargazing!"18. "May your new telescope open up a world of infinite possibilities and endless fascination. Enjoy your journey through the cosmos!"19. "Here's to your new gateway to the Universe! May your telescope gift lead you on an extraordinary adventure filled with celestial wonders. Happy exploring!"20. "Wishing you nights filled with starlight, moments of awe, and a deep connection to the wonders of the Universe. Enjoy your stargazing with your new telescope!"21. "May every moment spent with your new telescope gift be a reminder of the vastness and beauty of the Universe. Happy cosmic exploration!"22. "Here's to the gift of inspiration and the joy of unraveling the mysteries of the cosmos. Wishing you endless fascination and discovery with your new telescope!"23. "Wishing you clear skies, endless curiosity, and captivating discoveries with your new telescope. May the wonders of the Universe never cease to amaze you!"24. "May your new telescope be a window to the stars, allowing you to witness the mysteries of the Universe firsthand. Happy stargazing!" 25. "Here's to the gift of exploration, wonder, and enlightenment. May your new telescope gift lead you on an incredible journey through thecosmos. Enjoy your celestial adventures!"26. "Wishing you awe-inspiring nights, countless constellations, and a deeper understanding of the Universe with your new telescope. Happy exploring!"27. "May your new telescope gift unlock the secrets of the Universe and guide you on a cosmic journey to the stars. Enjoy the wonders that await you!"28. "Here's to a gift that will enchant and inspire you to reach for the stars. May your new telescope gift bring you endless joy and discovery. Happy stargazing!"29. "Wishing you a lifetime of celestial wonders and magical stargazing with your new telescope. May each observation be filled with awe and fascination."。

我对天文感兴趣英语作文

我对天文感兴趣英语作文I've always been fascinated by the stars and the mysteries of the universe. There's something so awe-inspiring about the vastness of space and the countless galaxies, planets, and stars that exist beyond our own.It's a constant reminder of how small we are in the grand scheme of things.Stargazing is one of my favorite pastimes. There's nothing quite like lying on a blanket and looking up at the night sky, trying to pick out constellations and marveling at the sheer number of stars that are visible on a clear night. It's a peaceful and humbling experience that never fails to leave me in awe.I love learning about the latest discoveries in astronomy. Whether it's a new exoplanet that has been found or a breakthrough in our understanding of black holes, I'm always eager to soak up as much knowledge as I can about the cosmos. It's amazing to think about how much we'velearned about the universe, and yet how much more there is still to discover.The beauty of the night sky has inspired countless works of art and literature, and it's easy to see why. There's a sense of wonder and mystery that comes with contemplating the stars, and it's no wonder that so many people have been captivated by them throughout history.It's a reminder of the power of nature to inspire and awe us.I hope to one day have the opportunity to see the stars from a different perspective perhaps by traveling to a remote location with minimal light pollution, or even by venturing into space myself. The idea of seeing the Earth from afar and experiencing weightlessness is incredibly exciting to me, and I can only imagine how profound an impact it would have on my appreciation for the cosmos.In the end, my interest in astronomy is driven by a deep-seated curiosity about the unknown. The universe is full of unanswered questions and unexplored territories,and the thought of delving into those mysteries is endlessly thrilling to me. It's a reminder that there is always more to learn and discover, and that the universe is a place of endless wonder and possibility.。

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a rXiv:as tr o-ph/38543v129Aug23SEARCHES FOR HIGH REDSHIFT GALAXIES USING GRA VITATIONAL LENSING J.Richard 1,R.Pello 1,J.-P.Kneib 1,2,D.Schaerer 1,3,M.R.Santos 2,R.Ellis 21O.M.P .,Laboratoire d’Astrophysique,UMR 5572,14Avenue E.Belin,31400Toulouse,France 2California Institute of Technology,105-24Caltech,Pasadena,CA 91125,USA 3Geneva Observatory,51Ch.des Maillettes,CH-1290Sauverny,Switzerland jrichard@ast.obs-mip.fr Abstract We present different methods used to identify high redshift (z >5)objects in the high-magniﬁcation regions of lensing galaxy clusters,taking advantage of very well constrained lensing models.The research procedures are explained and discussed.The detection of emission lines in the optical/NIR spectra,such as Lyman-alpha,allows us to determine the redshift of these sources.Thanks to the lensing magniﬁcation,it is possible to identify and to study more distant or intrinsically fainter objects with respect to standard ﬁeld surveys.Keywords:galaxies:formation,evolution,high-redshift,luminosity function,clusters :lensing —cosmology:observations Introduction The main purpose of looking at high redshift (z >5)objects is to get con-straints about the nature and the formation epoch of the ﬁrst sources in the Universe.The advent of 8-10m class telescopes,such as VLT and Keck,hasopened up this ﬁeld of study.Moreover,the use of clusters of galaxies as grav-itational telescopes can help a lot for this.Strong lensing effect in clusters has already enabled the detection of one of the most distant galaxies known up to now (Hu et al.2002),thanks to the gravitational magniﬁcation and despite the decrease in effective area of the survey.We present here two methods aimed at the detection of lyman-alpha sources behind galaxy clusters :ﬁrst a spectroscopic search along the critical lines of clusters,and then a photometric selection technique for very low metallicity starbursts (the so-called Population III objects,Loeb &Barkana 2001),using ultra-deep near infrared imaging.2Critical lines surveyUsing the LRIS spectrograph at Keck,we searched for Lyαemitters at red-shift2.5to6.8in the most magniﬁed parts of a sample of lensing clusters,selected for having well-constrained mass models.We scanned the regionslocated near the critical lines(Figure1),deﬁned as the lines of inﬁnite mag-niﬁcation for a given redshift,using a175"-long slit.Half of the area covered(4.2arcmin2)is at least magniﬁed by a factor of10at z=5.We systematically looked for every single emission line in the spectra,andwe conﬁrmed Lyαcandidates using HST images available for these clusters,optical photometry,and further spectroscopy at higher resolution,using ESI atKeck that can easily resolve the[OII]doublet,thus preventing this contamina-tion.We identiﬁed12Lyαcandidates,three of them lying in the redshift range∼4.6−5.6.One is a double image at z∼5.6which was analysed with more details by Ellis et.al(2001).The two-dimensionnal LRIS spectra,showingLyαemission lines,are presented inﬁgure1.Thanks to the strong lensing magniﬁcation,these results can give us con-straints on the luminosity function of emitters at4.6<z<5.6with Lyαluminosity1040<L<1042erg/s,which is a depth that was not reached by other surveys of Lyαemitters or Lyman Break Galaxies.This will be pre-sented in Santos et al.(2003,ApJ submitted).Figure1.On the left:zoom on the center part of the galaxy cluster Abell2218.The critical lines for z=5are shown as dashed lines,and the two regions scanned by the survey as rectangles. On the right:composite spectra of the three Lyαemitters(circled)found at z∼5−6.Searches for high redshift galaxiesusing gravitational lensing3 Looking for Population III objectsRecent models by D.Schaerer(2002,2003)for the Spectral Energy Distri-butions(SED)of Population III objects show that they may be currently ob-servable using8-10m telescopes,at the limits of conventional spectroscopy. The identiﬁcation of such objects should be possible thanks to their very strong emission lines,mainly Lyαand HeIIλ1640.In order toﬁnd these objects,the colors predicted by the same models can allow us to deﬁne a color-color region in the near-infrared diagram(J-H)vs(H-K’),where we can pick up candidates (Fig.2).By doing simulations with existing models,we found that we should not be contaminated by stars or z<8galaxies,even in the case of important redenning.As aﬁrst test of these selection criteria,we did very deep imaging(limiting magnitudes of J=25,H=24.5,K’=24,Vega system),with ISAAC on VLT,of two lensing clusters,taking advantage of the lensing magniﬁcation to help us detecting these faint objects.Preliminary resultsWe selected several(∼10)candidates per cluster,satisfying our selection criteria in the near-IR,and being undetected on available optical images.These objects have the expected magnitudes and SEDs of8<z<10Population III objects(Figure2),and are magniﬁed by2to4magnitudes thanks to the strong lensing effect.We used a modiﬁed version of the photometric software hyperz(Bolzonella et al.2000)toﬁnd the redshift distribution probability of our candidates with the spectra models quoted above.Figure2.Left:location,on the NIR color-color diagram(J-H)vs(H-K’),of the candidates found with the typical photometric errors(Vega system).The selection region for Population III objects is delimited by a solid line.Right:example of SED,combining infrared and optical photometry,for one of the candidates.Photometric redshift gives z∼9.As a preliminary result,we can try to compare the number of Population III objects per redshift that was expected to be detected in ourﬁeld with the upper4limit corresponding to our candidates,using a simple model of dark-matter halos distribution(Press&Schechter,1974),and4different models of IMF for PopIII galaxies(Figure3).Furthermore,we can estimate the efﬁciency of using strong lensing in thisﬁeld by plotting the expected number counts in a blankﬁeld of same size and depth.Weﬁnd that lensing is more efﬁcient at high redshifts(z>8),and that the number of candidates we found is consistent with some of the models we used.ConclusionsThe use of gravitational lensing is efﬁcient to detect more distant or intrinsi-cally fainter galaxies lying behind galaxy clusters:we can have constraints on luminosity functions at fainter scales,and the expected number of primordial objects in a clusterﬁeld is boosted at high redhsifts.Even if the candidates we found with our selection criteria are very faint,we should try to perform spectroscopy of the best ones with present day facilities. The detection of these sources is one of the major science cases for the next generation NIR instruments,like EMIR/GTC,KMOS/VLT or KIRMOS/Keck.Figure3.Number counts of PopIII objects per interval of0.1in z,expected to have K’<24in the ISAAC fov.The different curves correspond to different IMF models.The values obtained with gravitational lensing(solid curves)are boosted by a factor of10at z∼8−10regarding the one expected for a blankﬁeld(dashed curves).Overplotted is the upper limit of our survey. ReferencesBolzonella,M.,Miralles,J.M.,Pello,R.,2000,A&A,363,476Ellis,R.,Santos,M.R.,Kneib,J.-P.,Kuijken,K.,2001,ApJ,560,L119Hu,E.,et al.2002a,ApJ,568,L75Loeb,A.&Barkana,R.,2001,ARA&A,39,19Press,W.H.&Schechter,P.,1974,ApJ,187,425Santos,M.R.,Ellis,R.,Kneib,J.-P.,Richard,J.,Kuijken,K.,ApJ submittedSchaerer,D.2002,A&A,382,28Schaerer,D.2003,A&A,397,527Schaerer,D.&Pello R.,2001,astroph/0107274。