星系群和星系团的显著均匀性的意义
Implications of the remarkable homogeneity of galaxy groups and clusters
摘要：
我们测量的星系群和星系团的多样性与质量M> 1 E13/h Msun，在他们的星系人口的恒星形成历史，限制的质量尺度，在环境中重要的过程中发挥作用的星系演化的目的。我们考虑三个不同的组目录，以不同的方式选择，从斯隆数字巡天测光和光谱。对于每个系统，我们测量了在R200内的被动演化星系的比例，并且比Mr=-18（z<0.05）或Mr=-20（z<0.1）更亮。我们使用（u-g）和（r-i）星系的颜色来区分恒星形成和被动演化的星系。通过考虑从每个集群中观察到的成员数量中预期的二项分布，我们能够恢复该部分中的固有散射，或者对其值设置稳健的95%置信上限。被动星系分数的内在标准差与所有三个样本的大多数质量箱中<0.1的小值一致。没有强烈的趋势与质量;甚至组与M= 1 E13/h Msun是一致的，这样一个小的，内在的分布。我们比较这些结果与理论模型的吸积历史表明，如果环境中发挥作用，在改造星系，这种效果必须首先发生在质量尺度远低于丰富的集群，最多M= 1 E13 Msun。
英文摘要：
We measure the diversity of galaxy groups and clusters with mass M>1E13/h Msun, in terms of the star formation history of their galaxy populations, for the purpose of constraining the mass scale at which environmentally-important processes play a role in galaxy evolution. We consider three different group catalogues, selected in different ways, with photometry and spectroscopy from the Sloan Digital Sky Survey. For each system we measure the fraction of passively-evolving galaxies within R200 and brighter than either Mr=-18 (and with z<0.05) or Mr=-20 (and z<0.1). We use the (u-g) and (r-i) galaxy colours to distinguish between star-forming and passively-evolving galaxies. By considering the binomial distribution expected from the observed number of members in each cluster, we are able to either recover the intrinsic scatter in this fraction, or put robust 95% confidence upper-limits on its value. The intrinsic standard deviation in the fraction of passive galaxies is consistent with a small value of <0.1 in most mass bins for all three samples. There is no strong trend with mass; even groups with M=1E13/h Msun are consistent with such a small, intrinsic distribution. We compare these results with theoretical models of the accretion history to show that, if environment plays a role in transforming galaxies, such effects must occur first at mass scales far below that of rich clusters, at most M=1E13 Msun.
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