The Global Star formation History of Clusters of Galaxies

我们从文献中许多z=0 ~ 1之间的星系团的数据中发现，蓝光度与重子质量比随着红移而增加2-3倍。如果这被解释为蓝色亮度的变亮，那么变亮的数量与被动演化的椭圆星系相当。我们用斯巴鲁望远镜观测了两个z bbb101星系团，发现在假设星系被动演化的情况下，这些星系团（大多数被认为是椭圆星系）中明亮星系的光度函数（LF）与现今星系团的光度函数（LF）一致。另一方面，也发现在这些z bbb101星团中有相当一部分明亮的星系具有恒星形成活动。这些结果表明，星团中全球恒星形成的历史可以用星系的一级被动演化来近似，尽管单个星系的演化显得更为复杂。在这项研究中，我们假设星系团是封闭系统。然而，实际的星团是开放系统，通过周围星系的吸积来增加质量。在建模中考虑这种影响是未来的工作。

We find from data of many clusters of galaxies between z=0 and 1 in the literature that the blue luminosity to baryon mass ratio increases with redshift by a factor of 2-3. If this is interpreted as brightening of the blue luminosity, the amount of brightening is comparable to that of passively evolving elliptical galaxies.We observed two z>1 clusters with Subaru Telescope, and find that the luminosity function (LF) of bright galaxies in these clusters (most of them are thought to be elliptical galaxies) is consistent with the LF in the present day clusters if galaxies are assumed to evolve passively. On the other hand, it is also found that a significant fraction of bright galaxies in these z>1 clusters have star formation activity.These results show that the global star formation history in clusters can be approximated by the passive evolution of galaxies to first order, though the evolution of individual galaxies appears more complicated. In this study, we have assumed that clusters of galaxies are closed systems. However, actual clusters are open systems, increasing their mass by accretion of ambient galaxies. Taking account of this effect in modeling is future work.