Galaxies with Active Nuclei 有活动核的星系 Chapter 14: Galaxies with Active Nuclei 有活动核的星系

Active Galaxies 活动星系  “active galactic nuclei” (= AGN) 活动星系核 Galaxies with extremely violent energy release in their nuclei (pl. of nucleus). 核区活动剧烈（释放巨大能量）  “active galactic nuclei” (= AGN) 活动星系核 Up to many thousand times more luminous than the entire Milky Way; energy released within a region approx. the size of our solar system! 在太阳系大小的范围内，释放的能量可达银河系总能量的几千倍

Line Spectra of Galaxies 星系线光谱 Taking a spectrum of the light from a normal galaxy: 正常星系的光谱 The light from the galaxy should be mostly star light, and should thus contain many absorption lines from the individual stellar spectra. 多是恒星光，有很多吸收线

Seyfert Galaxies Very bright cores 非常亮的核 Emission line spectra 发射线光谱 Unusual spiral galaxies: 不寻常的漩涡星系 Very bright cores 非常亮的核 Emission line spectra 发射线光谱 Variability: ~ 50 % in a few months 光变 Most likely power source 最可能的能源: Accretion onto a supermassive black hole (~107 – 108 Msun) 超大质量黑洞吸积物质 NGC 1566 Circinus Galaxy NGC 7742

Interacting Galaxies 相互作用星系 Seyfert galaxy NGC 7674 Seyfert galaxy 3C219 Active galaxies are often associated with interacting galaxies, possibly result of recent galaxy mergers. 活动星系经常和相互作用星系有联系

Cosmic Jets and Radio Lobes 喷流和射电瓣 很多活动星系有很强的射电喷流 Hot spots: Energy in the jets is released in interaction with surrounding material 喷流的能量释放到与其相互作用的周围物质里，形成热点 Radio image of Cygnus A Material in the jets moves with almost the speed of light (“relativistic jets”相对论性喷流).

Formation of Radio Jets 射电喷流的形成 Jets are powered by accretion of matter onto a supermassive black hole. 喷流是由黑洞吸积物质产生的 Black Hole 黑洞 Accretion Disk 吸积盘 Twisted magnetic fields help to confine the material in the jet and to produce synchrotron radiation. 磁场束缚物质，产生射电辐射。

The Jets of M87 Jet: ~ 2.5 kpc long Jet: ~ 2.5 kpc long M87 = Central, giant elliptical galaxy in the Virgo cluster of galaxies Optical and radio observations detect a jet with velocities up to ~ 1/2 c. 喷流速度达到1/2光速。

The Dust Torus in NGC4261 尘埃环 Dust torus is directly visible with Hubble Space Telescope 哈勃空间望远镜直接观测到的尘埃环

Model for Seyfert Galaxies 模型 Gas clouds气体云 Jets 喷流 Emission lines 发射线 UV, X-rays 高能光子 Supermassive black hole 超大质量黑洞 Accretion disk 吸积盘 dense dust torus 尘埃环

The Origin of Supermassive Black Holes 超大质量黑洞的起源 Most galaxies seem to harbor supermassive black holes in their centers 大多数星系中心有黑洞. Fed and fueled by stars and gas from the near-central environment 吸积近处恒星和气体。

黑洞吸积恒星（视频）

The Discovery of Quasars 类星体的发现 The Discovery of Quasars 类星体的发现

First Quasar – 3C273 (1963) The discovery The third Cambridge (3C) catalog (1959) Radio sources Most are galaxies Some star-like sources (3C48, 3C273), but not stars.

First Quasar – 3C273 (1963) Solar Spectrum

First Quasar – 3C273 (1963) Solar Spectrum

First Quasar – 3C273 (1963) QUASAR: Quasi-stellar radio sources

First Quasar – 3C273 (1963) QUASAR: Quasi-stellar radio sources

First Quasar – 3C273 (1963) QUASAR: Quasi-stellar radio sources

The Discovery of Quasars 类星体的发现 The Quasar 3C273（第一个类星体） 光谱线红移非常大 红移 z = /0 = 0.158

First Quasar – 3C273 (1963) Redshift: Doppler Effect z ~ v/c QUASAR: Quasi-stellar radio sources Expending Universe Hubble's Law Once we realize the redshift, we knew other objects with similar spectra. Quasars are objects outside the Milky Way. point source large redshift highly variable rich with broad and narrow emission lines

Quasar Red Shifts 类星体的红移 Quasars have been detected at the highest redshifts, up to 最大红移的类星体 z ~ 6 z = 0 z = 0.178 z = 0.240 z = /0 z = 0.302 老公式 /0 = vr/c 只在低速（vr << c）情况下适用 z = 0.389

Seyfert Galaxies Spectrum of a galactic neucleus Quasars have hosts too. Spectrum of a galactic neucleus The galactic neucleus emits the same amount of energy as the rest of the galaxy.

Quasars are the neuclei of their host galaxies

Quasars 类星体 Active nuclei in galaxies with even more powerful central sources than Seyfert galaxies. 比Seyfert星系（更远）更强的活动星系核 Also show strong variability over time scales of a few months. 亮度随时间变化 （没有规律） Also show very strong, broad emission lines in their spectra. 光谱里有很强的发射谱线

Active Galactic Neuclei (AGN) Active Galactic Neuclei Family Quasar: Quasi-stellar radio source QSO: Quasi-stellar object (no radio emission) Seyfert galaxy LINERS: Low-ionization nuclear emission-line region BL Lac ... Active Galactic Neuclei (AGN) quasar=qso=AGN AGN dominates the host galaxy in energy output. The Milky Way is not an active galaxy.

AGN Structure

Studying Quasars 类星体研究 The study of high-redshift quasars allows astronomers to investigate questions of 利用高红移类星体可以研究： 1) Large scale structure of the universe 宇宙大尺度结构 2) Early history of the universe 早期宇宙历史 3) Galaxy evolution 星系演化 4) Dark matter 暗物质 Observing quasars at high redshifts 观测高红移的类星体  探测很远的距离（Gpc） Look-back times of many billions of years 回视时间达几十亿年  Universe was only a few billion years old! 宇宙年龄只有现在的1%

AGN Structure Major components: super massive black hole accretion disk emision line clouds/wind dusty torus jets Optical-UV-X-ray continua arise from the accretion disk (T ~ 104 – 105K).

Probing Dark Matter with High-z Quasars: Gravitational Lensing 高红移类星体探测引力透镜 星系团背后类星体的光线被星系团的质量（引力）改变方向  two images of the same quasar! 同一个类星体的两个象 Use to probe the distribution of matter in the cluster. 可以用来研究物质分布

Gravitational Lensing of Quasars 类星体的引力透镜 Gravitational Lensing of Quasars 类星体的引力透镜

AGN Structure Structures are spatially unresolved. How do we know the structure ?

AGN Structure Most Convincing Evidence: 1. Black Hole Mass Measurement 2. AGN Unified Model

Measure Black Hole Mass G － 引力常数 M(r)－轨道内天体总质量

Measure Black Hole Mass I: Nearby AGNs The Keperian motion of the accretion disk was detected using Very Long Baseline Interferometry (VLBI). Central mass is 4x107 solar mass. NGC4258

Measure Black Hole Mass II: Distant AGNs Same principle: Measure the velocity and distance of emission line clouds. line continuum V from emission line width.

Measure Black Hole Mass II: Distant AGNs Same principle: Measure the velocity and distance of emission line clouds. line r from echo mapping. continuum continuum line Time variability

Measure Black Hole Mass II: Distant AGNs Same principle: M ~ r V2/G Measure the velocity and distance of emission line clouds. line continuum Time variability

AGN Unified Model Two types of Seyfert galaxies: Seyfert 1 and Seyfert 2

AGN Unified Model Dusty torus Broad emission line region Fast moving Seyfert 2 Narrow emission line region Slow moving Seyfert 1

AGN Unified Model Seyfert 2, narrow line only Seyfert 2 Seyfert 1

AGN Unified Model Seyfert 2, narrow line only Seyfert 2 Seyfert 1

AGN Unified Model Seyfert 2, narrow line only Seyfert 2 Broad lines appear Seyfert 1