1、2018/6/21,,1,第六章 河外星系,研究历史星系分类 星系测量特殊星系 星 系 团 星系演化,http:/ ：银河是纯粹的大气现象，是地球发出的水蒸汽1609年，意大利天文学家伽利略把他新造的望远镜指向银河：银河是无数恒星的大集合银河是由恒星组成的研究太阳系，而很少有人关注银河系,2018/6/21,,3,1755年，普鲁士哲学家康德：银河是恒星构成的盘状物，恒星围绕某个中心公转被称为“星云”的模糊天体是和银河类似的 “宇宙岛”（island universes) 1781年法国天文学家C. Messier发表了包含110个星云表其中40个实际上是星系The Messier Catal
2、ogue (M51, M81)英国天文学家William Herschel 1786年、1789年和1802年三次出版星云和星团表，记录了2,500个星云和星团有些星云是不可分解的，放弃了星云是河外星系的主张,2018/6/21,,4,2018/6/21,,5,Herschel 假定恒星亮度相等，没有考虑尘埃影响,Sun,William Herschel, 20-foot reflector, 24-inch speculum metal mirror, in an altazimuth mounting, Bath, England, 1776.,2018/6/21,,6,仙女座大星系 (A
3、ndromeda Galaxy) M31,2018/6/21,,7,The Great Debate 1920年4月26日美国国家科学院,辩论焦点：宇宙的尺度 (M31)(1) “旋涡星云”的距离是多远？Nebulae (2) “旋涡星云”是恒星系统还是气体云？(3) “旋涡星云”在天球上的分布为什么有“隐带”？(4) 为什么“旋涡星云”的谱线出现红移？,“旋涡星云”是银河系内气体云，银河系就是整个宇宙。,宇宙是由无数类似银河系的星系构成的，“旋涡星云” 实际上是星系。,Harlow Shapley,Heber D. Curtis,2018/6/21,,8,沙普利：银河系对旋涡星云施加了一种未
4、知的排斥力，导致旋涡星云的隐带分布和退行现象。,柯蒂斯：有些旋涡星云的中心面有一条暗带。如果银河系也有类似的暗带，我们位于银河系的暗带中，如果旋涡星云是河外天体， 旋涡星云的分布出现隐带,由于观测数据中都存在较大的误差，这场大辩论当时没有结论！,沙普利错了,2018/6/21,,9,The Shapley-Curtis Debate (1920),MWG,MWG,Shapley,Curtis,The debate solved nothing!Questions in science are not resolved by debates, but by observations & expe
5、riments,2018/6/21,,10,哈勃的裁决,哈勃 (1889 - 1953)，美国天文学家。 1924年，利用当时最大2.5m望远镜哈勃分解出M31中几十个造父变星证实M31确实是一个恒星系统由造父变星周光关系估计M31的距离285 kpc(实际距离770 kpc)大于最远的球状星团的距离 (100 kpc) 。,因此M31必定是河外星系 !,1929年，哈勃发现河外星系视向退行速度v与距离d成正比 ，哈勃定律,2018/6/21,,11,Hubble Ultra Deep Field Image： 10平方角分10,000星系,月亮在天球上投影的视直径31角分,面积750平方角分
6、,2018/6/21,,12,2018/6/21,,13,第六章 河外星系,研究历史星系分类 星系测量特殊星系 星 系 团 星系演化,http:/ are the three major types of galaxies?,Hubble Deep Field,2018/6/21,,15,Hubble Ultra Deep Field,2018/6/21,,16,Hubble Ultra Deep Field,2018/6/21,,17,Hubble Ultra Deep Field,Spiral Galaxy,2018/6/21,,18,Elliptical Galaxy,Hubble Ul
7、tra Deep Field,Spiral Galaxy,2018/6/21,,19,Elliptical Galaxy,Hubble Ultra Deep Field,Elliptical Galaxy,Spiral Galaxy,2018/6/21,,20,Hubble Ultra Deep Field,Spiral Galaxy,Elliptical Galaxy,Elliptical Galaxy,2018/6/21,,21,Irregular Galaxies,Hubble Ultra Deep Field,Spiral Galaxy,Elliptical Galaxy,Ellipt
8、ical Galaxy,2018/6/21,,22,星系分类： Hubble Tuning Fork Scheme,2018/6/21,,23,椭圆星系 /透镜状星系/旋涡星系/棒旋星系/不规则星系,2018/6/21,,24,星族 (Stellar Population),1944年Walter Baade发现星系晕与核球中的恒星明显比盘中的恒星颜色偏红。Baade由此提出星族的概念：星族I、星族II,2018/6/21,,25,星族I恒星 年轻的、富金属恒星（金属丰度为太阳值的0.1-2.5倍）主要位于银盘中 ，绕银心作圆轨道运动 。如疏散星团。星族II恒星,年老的、贫金属恒星(金属丰度为
9、太阳值的0.001-0.03倍)主要位于银晕和核球中，以银心作为中心球对称分布绕银心作无规则的椭圆轨道运动。如球状星团。,2018/6/21,,26,不同星族天体的特征比较,2018/6/21,,27,椭圆星系 Elliptical galaxiesE,2018/6/21,,28,形状成圆球形或椭圆形按椭率大小的增加分为：E0、E1.E7八个次型n=10(a-b)/a a和b为椭圆半长轴和半短轴 中心区最亮，亮度向边缘递减,椭圆星系 (Elliptical galaxies，E),2018/6/21,,29,年老的、贫金属星族恒星构成椭圆星系没有星系盘，颜色偏红没有或仅有少量星际气体和尘埃恒星
10、作无规则的椭圆轨道运动 椭圆星系的大小和质量相差悬殊巨椭圆星系 106 pc, 1013M矮椭圆星系 103 pc, 107M,22 MV 18,2018/6/21,,30,2018/6/21,,31,2018/6/21,,32,一类具有旋涡结构的星系中心是球状或椭球状核球星系外面是扁平的星系盘从核球两端延伸出两条或两条以上螺旋状旋臂叠加在星系盘上星系盘外面是球状星系晕,旋涡星系 (Spiral galaxies，S),2018/6/21,,33,Spiral Galaxy,Disk 星系盘,Bulge核球,Halo 星系晕,2018/6/21,,34,Spheroidal Component
11、: bulge & halo, old stars,few gas clouds,Disk Component: stars of all ages,many gas clouds,2018/6/21,,35,Disk Component:stars of all ages,many gas clouds,Spheroidal Component:bulge & halo, old stars,few gas clouds,Red-yellow color indicates older star population,Blue-white color indicates ongoing st
12、ar formation,2018/6/21,,36,Disk Component:stars of all ages,many gas clouds,Spheroidal Component:bulge & halo, old stars,few gas clouds,Red-yellow color indicates older star population,Blue-white color indicates ongoing star formation,2018/6/21,,37,星族特征星系盘颜色偏蓝，星系晕和核偏红。在星系盘、特别是旋臂上主要是年轻、金属富的星族I恒星以及气体和
13、尘埃核球和星系晕主要由年老的星族恒星组成,21 MV 17,2018/6/21,,38,Circular Orbits in a Spiral Disk,Random Orbits in an Elliptical (or Spiral Bulge),2018/6/21,,39,分类：核球的大小和旋臂的缠卷程度Sa 中心区最大，旋臂紧卷Sb中心区较小，悬臂开展Sc中心区成为一个小亮核，悬臂松弛。,2018/6/21,,40,2018/6/21,,41,M51 grand design,NGC4414 flocculent,M101Multiple Arms,Arm Types,A grand
14、design spiral galaxy is a type of spiral galaxy with prominent and well-defined spiral arms A flocculent spiral is one that has patchy structures in its disk,2018/6/21,,42,2018/6/21,,43,2018/6/21,,44,棒旋星系 (Barred spiral galaxies，SB),2018/6/21,,45,由恒星组成的棒贯穿其核心部分的旋涡星系旋臂源于棒的两端按照棒的大小和旋臂的缠卷程度可以分为：SBa、SBb
15、、SBc三个次型SBa棒最大，旋臂缠卷最紧银河系可能是一个SBb或SBc型星系。,棒旋星系 (Barred spiral galaxies，SB),2018/6/21,,46,2018/6/21,,47,密度波理论：旋臂中的星不是一成不变的恒星有进有出川流不息而旋臂图案却保持不变旋臂不会缠卷起来,Stars & low density gas,Gas compression in density wave,New stars exit with old,2018/6/21,,48,透镜星系(Lenticular galaxies，S0) Has a disk like a spiral gal
16、axy but much less dusty gas (intermediate between spiral and elliptical),2018/6/21,,49,介于椭圆星系和旋涡星系的过渡型星系“无旋臂的盘星系”，外形像侧视的透镜根据核心是否有棒状结构，符号相应为S0或SB0透镜状星系与旋涡星系的主要差别是没有旋臂透镜状星系与椭圆星系的主要差别是有星系盘 星族主要由年老恒星组成，气体很少，类似E星系,透镜星系(Lenticular galaxies，S0),NGC 3115,2018/6/21,,50,NGC 2787 is classified as an SB0， a bar
17、red lenticular galaxy.,2018/6/21,,51,不规则星系(Irregular galaxies， Irr),Blue-white color indicates ongoing star formation,2018/6/21,,52,外形不规则，没有明显的核和旋臂，也没有旋转对称性分类：Irr I类有隐约可见、不规则的棒状结构；尘埃云不显著，偏蓝Irr II类具有无定型的外貌，带有明显的尘埃带，颜色偏黄年轻星族为主、气体含量多，质量不大， M1010M,M82,IC5152,18 MV 10,不规则星系(Irregular galaxies， Irr),2018/
18、6/21,,53,NGC 2363,2018/6/21,,54,2018/6/21,,55,www.public.asu.edu/rjansen/nfgs/,2018/6/21,,56,星系形态与波段有关；与对比度有关,2018/6/21,,57,更为客观的自动分类：模型参数面亮度分布旋涡星系: 椭圆星系: 一般函数:,NGC7331,2018/6/21,,58,Early type: high G, C; small A, M20,Concentration:the ratio of light within a circular or elliptical inner aperture t
19、o the light within an outer aperture,Asymmetry:quantifies the degree to which the light of a galaxy is rotationally symmetric,Gini Coefficient: the ratio of the area between the Lorenz curve and the curve of uniform equality where L(p) = p (shaded region) to the area under the curve of uniform equal
20、ity. G=A/A+B,M20: second-order moment of the brightest 20% of the galaxy,2018/6/21,,59,M20,G,more lightin fewer pix,more uniformsurface brightness,centrallyconcentrated,lessconcentrated,2018/6/21,,60,Spiral galaxies are often found in groups of galaxies(up to a few dozen galaxies),2018/6/21,,61,Elli
21、ptical galaxies are much more common in huge clusters of galaxies(hundreds to thousands of galaxies),2018/6/21,,62,Hubbles galaxy classes,SpheroidDominates,Disk Dominates,2018/6/21,,63,星系形态分类小结,2018/6/21,,64,What have we learned?,What are the three major types of galaxies?Spiral galaxies=Disk galaxi
22、es, elliptical galaxies, and irregular galaxiesSpirals have both disk and spheroidal components; ellipticals have no diskHow are galaxies grouped together?Spiral galaxies tend to collect into groups of up to a few dozen galaxiesElliptical galaxies are more common in large clusters containing hundreds to thousands of galaxies,2018/6/21,,65,Numbers of galaxies,There are around 41010 galaxies in the observable universe.Over 60% of galaxies are spiral, fewer than 30% are elliptical, and fewer than 15% are irregular.,
