New Constraints on the Luminosity Evolution of Spheroidal Galaxies in Distant Clusters

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Abstract
We investigate various probes of luminosity evolution in the rich cluster environment, concentrating in particular on the spheroidal (E/S0) galaxies, using a newly constructed catalog of morphologically classified Hubble Space Telescope (HST) images of galaxies observed in the cores of 13 clusters with redshifts 0.17 ≤ z ≤ 0.56. An important distinction of this study compared to earlier work is the availability for a substantial subset of our HST fields of new near-infrared ground-based photometry, which we have used to select and study the various populations. We find no significant change in the characteristic luminosity, M*K, of the spheroidal populations at redshifts of 0.31 and 0.56. As a more sensitive probe of luminosity evolution, we analyze the surface photometry of our HST-classified ellipticals by deriving effective metric radii, Re, and mean effective surface brightnesses, μe. At the standard condition corresponding to Re = 1 kpc, we find convincing evidence of evolutionary brightening in both rest frame B and K light, consistent with model predictions based on the passive evolution of stellar populations.
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