The Possible z=0.83 Precursors of z=0, M* Early-Type Cluster Galaxies
Kelson, D. D.; Ford, H. C.; Demarco, R.; Rosati, P.; Illingworth, G. D.; Blakeslee, J. P.; Franx, M.; Holden, B. P.; Postman, M.; Homeier, N.; Tran, K. -V. H.
United States, Netherlands, Germany
Abstract
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 1011.1 Msolar (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.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 9919 and 9290.