The Buildup of the Red Sequence in Galaxy Clusters since z ∼ 0.8

We study the rest-frame (U - V) color-magnitude relation in four clusters at redshifts 0.7-0.8, drawn from the ESO Distant Cluster Survey (EDisCS). We confirm that the red-sequence galaxies in these clusters can be described as an old, passively evolving population, and we demonstrate that, by comparison with the Coma Cluster, there has been significant evolution in the stellar mass distribution of red-sequence galaxies since z ∼ 0.75. The EDisCS clusters exhibit a deficiency of low-luminosity passive red galaxies. Defining as "faint" all galaxies in the passive evolution-corrected range 0.4 ≳ L/L* ≳ 0.1, the luminous-to-faint ratio of red-sequence galaxies varies from 0.34 ± 0.06 for the Coma Cluster to 0.81 ± 0.18 for the high-redshift clusters. These results exclude a synchronous formation of all red-sequence galaxies and suggest that a large fraction of the faint red galaxies in current clusters moved on to the red sequence relatively recently. Their star formation activity presumably came to an end at z ≲ 0.8.