活动星系
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In type II Seyfert galaxies the denser gas is missing or obscured.
Brightness varies on timescale of months → compact nucleus
3C 84的射电变化
The activity of some Seyfert galaxies may result from galaxy interactions.
Radio emission is produced by high-speed electrons in magnetic fields through synchrotron radiation.
Movement of radio galaxies causes different appearance.
Radiation power ~γ2B2β2, whereβ= v/c, γ= (1-β2)-1/2.
Beamed radiation along the particle’s motion with
half-opening angleα≈1/γ.
Power-law spectrum
(3) Unusual structure Bright nucleus, jets and irregular appearance
non-thermal radiation, with peak energy at far-infrared wavelength.
Synchrotron Radiation 同步加速辐射
Continuum radiation from high-speed charged particles, such as electrons, as they are accelerated in a strong magnetic field.
(1) High overall luminosities
Milky Way
X-ray luminosity
1
Radio galaxies
100-5,000
Seyfert galaxies 300-7×104 Quasars (3C 273) 2.5×106
Optical luminosity
1
2
infrared radiation. Usually elliptical galaxies.
3C 279
Non-thermal synchrotron radiation.
Most of them are elliptical galaxies, usually the brightest, largest ones in galaxy clusters.
Appearance
Core-halo type: the radio images are comparable or slightly smaller than their optical images; most of the radio emission comes form the nucleus.
NGC 5728的地面和空间观测
Comparison: Seyfert Galaxies and Star Burst Galaxies
Seyfert galaxy NGC 7742
Starburst Galaxy M94
On the basis of spectrum, Seyfert galaxies are classified as type I or II. In a type I spectrum, the allowed lines are broad (corresponding to a velocity of ~104 kms-1 ), and much broader than the fo的逐 次深度曝光像
NGC 1566
Almost all Seyfert galaxies are spirals. About 1% of all bright spiral galaxies are Seyfert galaxies. The luminosities of their nuclei are about ~1043-1045 ergs-1, of the same order as all the rest of the galaxy.
Normal galaxies z Blackbody radiation with peak
energy at optical wavelength z Radiation mainly comes from
stars inside galaxies. Active galaxies z Non-stellar radiation z Thermal (infrared) radiation +
第八章 活动星系
(Chapter 25)
§8.1 活动星系与活动星系核 §8.2 引力透镜和视超光速运动 §8.3 活动星系核的理论模型
§8.1 活动星系与活动星系核
1. Signs of activity 绝大部分星系是正常星系，但也有部分星系表 现出强烈的活动性，称为活动星系 (active galaxies)。在观测上分为下面几种： Radio galaxies 射电星系 Seyfert galaxies 赛弗特星系 BL Lac objects 蝎虎天体 Quasars 类星体
赛弗特星系与正常 星系发射线的比较
In type II, all allowed and forbidden lines are similar and narrower (≤103 kms-1) .
Seyfert I
Seyfert II
The reason for this difference is thought to be that the allowed lines are formed in denser gas near the nucleus (broad line region), and the forbidden lines in more diffuse gas further out (narrow line region).
The system may appear to us as either a lobe or a core–halo radio galaxy, depending on our location
with respect to the jets and lobes.
3. Seyfert Galaxies
Named after Carl Seyfert, who discovered them in 1943. Their most important characteristics are a bright, pointlike central nucleus and a spectrum showing broad emission lines.
Centaurus A (NGC 5128)
射电像 ：双瓣结构 光学像：尘埃带
NGC 1265: Head-Tail Radio galaxy
0313-192: The Wrong Spiral Galaxy
(2) Theoretical Model
Energy is fired out from the nucleus in the form of narrow, high-speed jets that travel into the intergalactic medium and become extended lobes.
Radio luminosity
1
2,000-2×106
2
20-2×106
250
6×106
Bright extragalactic radio sources
Normal galaxies
Optical
Quasar PKS 1127-145
X-ray
(2) Non-thermal radiation
Cygnus A with two-lobe structure
(1) Characteristics
Most active galaxies are radio galaxies.
Radio luminosities ( ~1042-1045 ergs-1 ) much higher than those of normal galaxies ( ~10371039 ergs-1 ).
(4) High, rapid variability
Variability timescale: several days to one year →the size of the power source is smaller than 1 light year.
(5) Strong emission lines and polarized emission
马卡良315
4. BL Lac Objects, Blazars
原型：蝎虎座BL （1929 年发现）。恒星状，有 暗弱包层。
Non-thermal continuum with very weak or no emission lines.
Most energy emitted inγ-ray, strong radio,
Double-lobe type: extended structure (as long as 1 Mpc); the radio energy is released from the radio lobes.
M86 Centaurus A
M87
The giant elliptical galaxy in Virgo cluster. The first galaxy found to have jets. The jet is about 2 kpc long and is made up of a series of distinct “blobs”.
2. Radio Galaxies
Active galaxies that emit most of their energy in the radio portion of the electromagnetic spectrum. Historical perspective In 1960s, British radio astronomers finished compiling the 3rd Cambridge (3C) catalog of radio sources. Many bright radio sources in the catalog were found to have optical counterparts (galaxies). They are both point-like and extended, and are called radio galaxies.
Statistics of Active Galaxies
Only 2% of all galaxies are active galaxies, bright active galaxies are more common at great distances. Most active galaxies are ellipticals. The high luminosities of active galaxies implies a short lifetime, so active galaxies must represent a passing stage in the evolution of normal galaxies, rather than form a separate class of galaxies.
Brightness varies on timescale of months → compact nucleus
3C 84的射电变化
The activity of some Seyfert galaxies may result from galaxy interactions.
Radio emission is produced by high-speed electrons in magnetic fields through synchrotron radiation.
Movement of radio galaxies causes different appearance.
Radiation power ~γ2B2β2, whereβ= v/c, γ= (1-β2)-1/2.
Beamed radiation along the particle’s motion with
half-opening angleα≈1/γ.
Power-law spectrum
(3) Unusual structure Bright nucleus, jets and irregular appearance
non-thermal radiation, with peak energy at far-infrared wavelength.
Synchrotron Radiation 同步加速辐射
Continuum radiation from high-speed charged particles, such as electrons, as they are accelerated in a strong magnetic field.
(1) High overall luminosities
Milky Way
X-ray luminosity
1
Radio galaxies
100-5,000
Seyfert galaxies 300-7×104 Quasars (3C 273) 2.5×106
Optical luminosity
1
2
infrared radiation. Usually elliptical galaxies.
3C 279
Non-thermal synchrotron radiation.
Most of them are elliptical galaxies, usually the brightest, largest ones in galaxy clusters.
Appearance
Core-halo type: the radio images are comparable or slightly smaller than their optical images; most of the radio emission comes form the nucleus.
NGC 5728的地面和空间观测
Comparison: Seyfert Galaxies and Star Burst Galaxies
Seyfert galaxy NGC 7742
Starburst Galaxy M94
On the basis of spectrum, Seyfert galaxies are classified as type I or II. In a type I spectrum, the allowed lines are broad (corresponding to a velocity of ~104 kms-1 ), and much broader than the fo的逐 次深度曝光像
NGC 1566
Almost all Seyfert galaxies are spirals. About 1% of all bright spiral galaxies are Seyfert galaxies. The luminosities of their nuclei are about ~1043-1045 ergs-1, of the same order as all the rest of the galaxy.
Normal galaxies z Blackbody radiation with peak
energy at optical wavelength z Radiation mainly comes from
stars inside galaxies. Active galaxies z Non-stellar radiation z Thermal (infrared) radiation +
第八章 活动星系
(Chapter 25)
§8.1 活动星系与活动星系核 §8.2 引力透镜和视超光速运动 §8.3 活动星系核的理论模型
§8.1 活动星系与活动星系核
1. Signs of activity 绝大部分星系是正常星系，但也有部分星系表 现出强烈的活动性，称为活动星系 (active galaxies)。在观测上分为下面几种： Radio galaxies 射电星系 Seyfert galaxies 赛弗特星系 BL Lac objects 蝎虎天体 Quasars 类星体
赛弗特星系与正常 星系发射线的比较
In type II, all allowed and forbidden lines are similar and narrower (≤103 kms-1) .
Seyfert I
Seyfert II
The reason for this difference is thought to be that the allowed lines are formed in denser gas near the nucleus (broad line region), and the forbidden lines in more diffuse gas further out (narrow line region).
The system may appear to us as either a lobe or a core–halo radio galaxy, depending on our location
with respect to the jets and lobes.
3. Seyfert Galaxies
Named after Carl Seyfert, who discovered them in 1943. Their most important characteristics are a bright, pointlike central nucleus and a spectrum showing broad emission lines.
Centaurus A (NGC 5128)
射电像 ：双瓣结构 光学像：尘埃带
NGC 1265: Head-Tail Radio galaxy
0313-192: The Wrong Spiral Galaxy
(2) Theoretical Model
Energy is fired out from the nucleus in the form of narrow, high-speed jets that travel into the intergalactic medium and become extended lobes.
Radio luminosity
1
2,000-2×106
2
20-2×106
250
6×106
Bright extragalactic radio sources
Normal galaxies
Optical
Quasar PKS 1127-145
X-ray
(2) Non-thermal radiation
Cygnus A with two-lobe structure
(1) Characteristics
Most active galaxies are radio galaxies.
Radio luminosities ( ~1042-1045 ergs-1 ) much higher than those of normal galaxies ( ~10371039 ergs-1 ).
(4) High, rapid variability
Variability timescale: several days to one year →the size of the power source is smaller than 1 light year.
(5) Strong emission lines and polarized emission
马卡良315
4. BL Lac Objects, Blazars
原型：蝎虎座BL （1929 年发现）。恒星状，有 暗弱包层。
Non-thermal continuum with very weak or no emission lines.
Most energy emitted inγ-ray, strong radio,
Double-lobe type: extended structure (as long as 1 Mpc); the radio energy is released from the radio lobes.
M86 Centaurus A
M87
The giant elliptical galaxy in Virgo cluster. The first galaxy found to have jets. The jet is about 2 kpc long and is made up of a series of distinct “blobs”.
2. Radio Galaxies
Active galaxies that emit most of their energy in the radio portion of the electromagnetic spectrum. Historical perspective In 1960s, British radio astronomers finished compiling the 3rd Cambridge (3C) catalog of radio sources. Many bright radio sources in the catalog were found to have optical counterparts (galaxies). They are both point-like and extended, and are called radio galaxies.
Statistics of Active Galaxies
Only 2% of all galaxies are active galaxies, bright active galaxies are more common at great distances. Most active galaxies are ellipticals. The high luminosities of active galaxies implies a short lifetime, so active galaxies must represent a passing stage in the evolution of normal galaxies, rather than form a separate class of galaxies.