The Global Star formation History of Clusters of Galaxies

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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.