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1、2018/10/21,,1,第六章 河外星系,研究历史 星系分类 星系测量 特殊星系：活动星系 星 系 团 星系演化,http:/ GOALS,活动星系和正常星系主要区别是什么？赛弗特星系、射电星系、类星体特征？ 活动星系的中心能源机制和统一模型？活动星系的如何形成和星系演化理论？,2018/10/21,,3,定义：具有明显的剧烈活动的一类星系星暴星系：内部有巨大的恒星形成的爆发区。它的特征是红外光度明显高于光学光度活动星系核：星系中心区域有一个极小而极亮的核；有强的非热连续谱 活动星系的数量约为正常星系总数的1%,活动星系,2018/10/21,,4,活动星系和正常星系能谱分布不同中心能源机
2、制差异,2018/10/21,,5,星暴星系 Starburst Galaxies,星系中有巨大的恒星形成的爆发区 特征是红外光度明显高于光学光度普通星系也形成恒星,但是形成的速度很慢. 星暴星系中,恒星的形成是非常剧烈,2018/10/21,,6,星暴星系中恒星形成剧烈，将在较短时间内(less than a billion years )消耗掉其内部的气体,starbursts are temporary,2018/10/21,,7,星暴星系中形成很多大质量恒星，他们演化到晚期发生超新星爆发，将产生星系风,M82 is the archetypal starburst galaxy.,20
3、18/10/21,,8,A galactic wind in a small galaxy can drive away most of its gas,2018/10/21,,9,星暴星系主要特征：如果以现在的恒星形成率(SFR)持续的形成恒星，将在远远短于宇宙年龄(13.7Gyr)的时标内消耗掉其内部气体。This is sometimes referred to as a “true“ starburst. 如果以现在的恒星形成率(SFR)持续的形成恒星， 其恒星形成时标也远小于其动力学时标 (perhaps one rotation period in a disk type gala
4、xy). The current SFR, normalised by the past-averaged SFR is much greater than unity,2018/10/21,,10,星暴的触发机制,星系的相互作用两个星系的并合,2018/10/21,,11,活动星系核 active galactic nucleus (AGN),An AGN is a compact region at the centre of a galaxy which has a much higher than normal luminosity over some or all of the el
5、ectromagnetic spectrum. A galaxy hosting an AGN is called an active galaxy.,2018/10/21,,12,活动星系核分类,Radio-loud objects a contribution from the jet(s) and the lobes they inflate dominates the luminosity of the AGN Radio-loud quasars ：射电类星体 BL Lac objects ：蝎虎天体 Radio galaxies ：射电星系Radio-quiet objects a
6、re simpler since jet and jet-related emission can be neglected. Low-ionization nuclear emission-line regions (LINERs) ：低电离核发射区 Seyfert galaxies ：赛弗特星系 Radio-quiet quasars/QSOs：射电宁静类星体,2018/10/21,,13,活动星系核特点,能量极高的星系，中心是一个超大黑洞 辐射绝大部分来自星系核，其他部分弱观测特点： 有的有快速光变，时标为几小时至几年 有的有明显的爆发现象，如喷流（Jet） 有的光谱中有宽的发射线，如H
7、a谱线,2018/10/21,,14,非热辐射,正常星系：恒星黑体辐射，热辐射AGN：非热辐射，SED峰值在FIR,2018/10/21,,15,Bright nucleus, jets and irregular appearance,2018/10/21,,16,High, rapid variability,光变时标: several days to one year size of the power source 1 lyr,2018/10/21,,17,AGN光谱：强的发射线和偏振,2018/10/21,,18,射电星系 Radio galaxy,通常指发出强烈的射电辐射（比一般的
8、星系强一百到一百万倍）的星系 射电星系大多为椭圆星系、巨椭圆星系和超巨椭圆星系,2018/10/21,,19,M87长时间曝光短时间曝光射电观测NIR观测,2018/10/21,,20,发出强烈的射电辐射(比一般的星系强102106倍) 的星系,射电：( 1042-1045 ergs-1 ) 正常：(1037-1039 ergs-1) 射电连续谱一般为幂律谱，且有偏振，谱指数平均为0.75具有非热性质，起源于相对论性电子在磁场中运动时产生的同步加速辐射射电星系的射电形态多样，可分为致密型、核晕型、双瓣型、头尾型和包含多个子源的复杂形,射电星系特征,2018/10/21,,21,1954 Cyg
9、nus A identified with a 17.5 mag galaxy strong radio sources can be optically faint!,1962 - 3C 273 identified with a star-like object with peculiar spectrum,1931 Karl Jansky discovers radio emission from the Galaxy,2018/10/21,,22,NGC 5128 (Cen A) radio galaxy at about 2.5 Mpc. HST image + VLA (6cm)
10、image,2018/10/21,,23,2018/10/21,,24,M 87 (Virgo A),The first galaxy found to have jets,2018/10/21,,25,Radio emission is produced by high-speed electrons in magnetic fields through synchrotron radiation,The system may appear to us as either a lobe or a corehalo radio galaxy, depending on our location
11、 with respect to the jets and lobes.,2018/10/21,,26,HST观测到的从活动星系M87 (射电星系)中心喷出的一个长度为5000光年的喷流 The synchrotron radiation of the jet (blue) contrasts with the starlight from the host galaxy (yellow).,2018/10/21,,27,2018/10/21,,28,赛弗特星系 Seyfert Galaxies,极亮的核区高电离发射线谱由谱线宽度分Sy1和Sy2named after Carl Seyfert
12、, 1943年首次发现了这类星系,2018/10/21,,29,1943 Carl Seyfert survey of galaxies with star-like nuclei & bright emission lines,NGC 7742 is a spiral galaxy with a prominent yellow nucleus surrounded by spiral arms containing many young, hot blue stars. It is a Seyfert galaxy, and first studied by astronomer Carl
13、 Seyfert in the 1940s.,2018/10/21,,30,NGC 4151的逐次深度曝光图像,Seyfert星系图像深度观测显示其为旋涡星系,2018/10/21,,31,2018/10/21,,32,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
14、 rest of the galaxy.,Seyfert星系多为旋涡星系 射电星系多为椭圆星系,2018/10/21,,33,Sy2 103 kms-1,Sy1 104 kms-1,Type I Seyferts 宽的光谱发射线， velocities around/high 1000 km/s. Type II Seyferts 窄的光谱发射线，have very low velocities,Seyfert galaxies 分类,2018/10/21,,34,Starburst galaxy M94,Seyfert galaxy NGC 7742,核更亮，宽发射线,2018/10/21,
15、,35,蝎虎座BL型天体 BL Lac Objects,BL Lac Galaxies, which are also called blazars, were misnamed. The first one discovered was given a star name (BL Lac), in particular a name associated with stars that change brightness. these are actually galaxies with very bright central regions, so bright that they look like a bright star when seen at great distances.亮核状天体，谱线很弱或无、具有快速光变,
