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从斯莱弗的发现到哈勃定律问世
早在1912年到1914年间,美国洛威尔天文台的斯莱弗(V.M.Slipher)观测了13个星云的光谱,发现其中11个存在红移现象,说明这些星云相对于地球在远离。1922年2月,斯莱弗发表了多个旋涡星云的视向速度数值表,进一步证实了其观测结果。当时,人们还不知道这些星云是在银河系之外的河外星系。1923年, 相似文献
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Jiu-Li Li Xu Zhou Jun Ma Jian-Sheng ChenNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2004,4(2):143-152
Based on the large field multicolor observations of Beijing-Arizona-Taiwan-Connecticut (BATC) program, we obtain the spectral energy distribution (SED) for individual regions of M81. We study the structure and evolution of M81 with an evolutionary population synthesis (EPS) model, PEGASE. We find that the exponentially deceasing star formation rate (SFR) with star formation scale 3 Gyr (hereafter Exp, τ=3 Gyr) gives the best agreement between the model predictions and the observed SEDs. We then obtain the structure, age distribution and evolutionary history of M81. There is a clear age gradient between the central and outer regions. The populations in the central regions are older than 7 Gyr,those in the outer regions are younger, at about 4.5 Gyr. The youngest components in the spiral arms have ages of about 2.5 Gyr or less. 相似文献
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