Evolution of Cluster Elliptical Galaxies

We have used deep optical and infrared imaging to study the E/S0 galaxies in the central regions of eight intermediate-redshift (0.40 < z < 0.48) clusters. We find that the luminosity function for red galaxies with -25.6 < MV < -17.6 (?M = 0.2, ?? = 0, and H0 = 50 km s-1 Mpc-1) in the clusters' red sequence are well described by a Schechter function for all clusters. In spite of the fact that the clusters span a wide range in richness and X-ray luminosities, all the cluster luminosity functions are consistent with a single value for their characteristic magnitude (M*). The value of M* at z = 0.45 appears brighter than that observed in local clusters (?M = -0.94 ? 0.41), in agreement with models of passive evolution and with studies of surface brightness and fundamental plane at these redshifts. We have also observed a color change in the rest-frame (U-V) and (V-H) colors, as compared to local galaxies. We find that most of the popular simple stellar population models fail to account for this color evolution vector with the discrepancy mainly in the optical-infrared color. However, the rest-frame (U-V) color change seems to be well described by these simple models, and it can be used to estimate the ages of the stellar populations in these galaxies. We find that the stars in the E/S0 galaxies at z = 0.45 must have been formed at z 1 for solar or supersolar metallicities.