6河外星系-1.ppt

1、2020/7/6,1,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,2020/7/6,2,研究历史,公元前5世纪，希腊哲学家德谟克利特：银河是由无数恒星所构成，太暗而不能区分 公元前3世纪，希腊哲学家亚里士多德 ：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,2020/7/6,3,1755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 univ

2、erses) 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 Catalogue (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,2020/7/6,4,2020/7/6,5,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, i

3、n an altazimuth mounting, Bath, England, 1776.,2020/7/6,6,仙女座大星系 (Andromeda Galaxy) M31,2020/7/6,7,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

4、上是星系。,Harlow Shapley,Heber D. Curtis,2020/7/6,8,沙普利：银河系对旋涡星云施加了一种未知的排斥力，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,2020/7/6,9,The Shapley-Curtis Debate (1920),MWG,MWG,Shapley,Curtis,The debate solved nothing! Questions i

5、n science are not resolved by debates, but by observations small A, M20,Concentration:the ratio of light within a circular or elliptical inner aperture to the light within an outer aperture,Asymmetry:quantifies the degree to which the light of a galaxy is rotationally symmetric,Gini Coefficient: the

6、 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 equality. G=A/A+B,M20: second-order moment of the brightest 20% of the galaxy,2020/7/6,59,M20,G,more light in fewer pix,more uniform surface brightness,

7、centrally concentrated,less concentrated,2020/7/6,60,Spiral galaxies are often found in groups of galaxies (up to a few dozen galaxies),2020/7/6,61,Elliptical galaxies are much more common in huge clusters of galaxies (hundreds to thousands of galaxies),2020/7/6,62,Hubbles galaxy classes,Spheroid Do

8、minates,Disk Dominates,2020/7/6,63,星系形态分类小结,2020/7/6,64,What have we learned?,What are the three major types of galaxies? Spiral galaxies=Disk galaxies, elliptical galaxies, and irregular galaxies Spirals have both disk and spheroidal components; ellipticals have no disk How are galaxies grouped together? Spiral galaxies tend to collect into groups of up to a few dozen galaxies Elliptical galaxies are more common in large clusters containing hundreds to thousands of galaxies,2020/7/6,65,Numbers of galaxies,There are around 410