Colors of Luminous Bulges in Cluster MS 1054-03 and Field Galaxies at Redshifts z~0.83

Abstract

Using Hubble Space Telescope images, we separate the bulgelike (dubbed ``pbulge'') and disklike (``pdisk'') components of 71 galaxies in the rich cluster MS 1054-03 and of 21 in the field. Our key finding is that luminous pbulges are very red, with rest-frame U-B~0.45, while predicted colors are bluer by 0.20 mag. Moreover, these very red colors appear to be independent of environment, pbulge luminosity, pdisk color, and pbulge fraction. These results challenge any model of hierarchical galaxy formation that predicts the colors of distant (z~0.8) luminous field and cluster bulges will differ. Our findings also disagree with other claims that 30% to 50% of bright bulges and elliptical galaxies at z~1 are very blue (U-B<=0).

Based on observations obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration; made with the NASA/ESA Hubble Space Telescope, obtained from the data archive 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 and associated with proposals GO-7372, GTO-5090, and GTO-5109.