EVOLUTION OF GALAXIES IN VERY HIGH REDSHIFT CLUSTERS

clusters of galaxies are unique laboratories for studying the evolution of galaxies out to large redshifts, providing large numbers of galaxies at a common distance. our current knowledge of cluster galaxy evolution is mostly based on observations at z < 0.5. the number of blue galaxies in clusters is increasing with redshift (the butcheroemler effect). spectroscopy and hst imaging have shown that these are mainly star forming disc galaxies, and even some of the redder cluster members (the e+a galaxies) show signs of recent strong star formation. at higher redshifts (z>0.8), only a handful of clusters are known. our team has identified clusters with 0.8 < z < 1.2, using radio galaxies as signposts pointing to rich environments. these clusters contain a population of galaxies undergoing strong star formation, but perhaps more surprisingly, a large fraction of galaxies is extremely red ellipticals, showing remarkably little evolution even at times when the universe was virgul40% of its present age. using isocam, we propose to study both the most actively star forming cluster galaxies and the oldest, most quiescent ellipticals. we will: (i) trace starburst activity in the most active galaxies by measuring midir fluxes and color temperatures from warm dust emission using the lw2 and lw10 filters, and investigate the role played by mergers in triggering the activity. (ii) constrain the ages and epoch of formation for the reddest population of galaxies using lw1 observations to measure fluxes near the restframe 1.6 micron peak in the stellar spectral energy distribution. age determinations for these high redshift galaxies can constrain the cosmological parameters h0 and q0. the clusters around 3c265, 3c184, 3c280, 3c210, and 3c324 (z0.81, 0.99, 1.00, 1.15, 1.2) extend beyond the redshift limits of existing optical and xray surveys, providing a unique sample for probing the early era of clus trun [truncated!, Please see actual data for full text]