The evolution of early-type red galaxies with the GEMS survey:: Luminosity-size and stellar mass-size relations since z=1

We combine imaging from the Hubble Space Telescope Advanced Camera for Surveys, as part of the GEMS ( Galaxy Evolution from Morphologies and SEDs) survey, with redshifts and rest-frame quantities from COMBO-17 to study the evolution of morphologically early-type galaxies with red colors since z = 1. From 0.degrees 5; 0.degrees 5 imaging, we draw a large sample of 728 galaxies with centrally concentrated radial profiles (i.e., n >= 2.5 from Sersic fits) and rest-frame ( U - V) colors on the red sequence. We explore how the correlations of rest-frame V-band luminosity and of stellar mass with intrinsic half-light size change over the last half of cosmic time. By appropriate comparison with the well-defined local relations from the Sloan Digital Sky Survey, we find that the luminosity-size and stellar mass - size relations evolve in a manner that is consistent with the passive aging of ancient stellar populations. By itself, this result is consistent with a completely passive evolution of the red early-type galaxy population. If instead, as demonstrated by a number of recent surveys, the early-type galaxy population builds up in mass by roughly a factor of 2 since z similar to 1, our results imply that new additions to the early-type galaxy population follow similar luminosity-size and stellar mass - size correlations, compared to the older subset of early-type galaxies. Adding early-type galaxies to the red sequence through the fading of previously prominent disks appears to be consistent with the data. Through comparison with models, the role of dissipationless merging is limited to < 1 major merger on average since z 1 for the most massive galaxies. Predictions from models of gas-rich mergers are not yet mature enough to allow a detailed comparison to our observations. We find tentative evidence that the amount of luminosity evolution depends on galaxy stellar mass, such that the least massive galaxies show stronger luminosity evolution compared to more massive early types. This could reflect a different origin of low-mass early-type galaxies and/or younger stellar populations; the present data are insufficient to discriminate between these possibilities.