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 1054-03 andRX J0152.7-1357, two X-ray selected clusters of galaxies at z=0.83. Our stellarmass estimates, from spectral energy distribution fitting, reproduce thedynamical masses as measured from velocity dispersions and half-light radiiwith a scatter of 0.2 dex in the mass for early-type galaxies. When we restrictour sample of members to high stellar masses, > 1e11.1 Msun (M* in theSchechter mass function for cluster galaxies), we find that the fraction ofearly-type galaxies is 79 +/- 6% at z=0.83 and 87 +/- 6% at z=0.023 for theComa cluster, consistent with no evolution. Previous work withluminosity-selected samples finds that the early-type fraction in rich clustersdeclines from =~80% at z=0 to =~60% at z=0.8. The observed evolution in theearly-type fraction from luminosity-selected samples must predominately occuramong sub-M* galaxies. As M* for field and group galaxies, especiallylate-types, is below M* for clusters galaxies, infall could explain most of therecent early-type fraction growth. Future surveys could determine themorphological distributions of lower mass systems which will confirm or refutethis explanation.Comment: 5 pages in emulate ApJ format with three color figures. Accepted for publication in ApJ Letters, v642n2. Updated to correct grammatical and typographic errors found by the journa