The Possible z = 0.83 Precursors of z = 0, M * Early-Type Cluster Galaxies

We examine the distribution of stellar masses of galaxies in MS 1054.4-0321 and Cl 0152.7-1357, two X-ray-selected clusters of galaxies at z = 0.83. Our stellar mass estimates, from spectral energy distribution fitting, reproduce the dynamical masses as measured from velocity dispersions and half-light radii with a scatter of 0.2 dex in the mass for early-type galaxies. When we restrict our sample of members to high stellar masses, those over 10 11.1 M ☉ ( M * in the Schechter mass function for cluster galaxies), we find that the fraction of early-type galaxies is 79% ± 6% at z = 0.83 and 87% ± 6% at z = 0.023 for the Coma Cluster, consistent with no evolution. Previous work with luminosity-selected samples has found that the early-type fraction in rich clusters declines from ≃80% at z = 0 to ≃60% at z = 0.8. The observed evolution in the early-type fraction from luminosity-selected samples must predominantly occur among sub- M * galaxies. As M * for field and group galaxies, especially late types, is below M * for cluster galaxies, infall could explain most of the recent growth in the early-type fraction. Future surveys could determine the morphological distributions of lower mass systems, which would confirm or refute this explanation.