Contents of: VI/111/./abstract/OLEFEVRE_OLF_3CCL.abs

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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 Butcher-Oemler 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  40% 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 mid-IR 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 rest-frame 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
(z=0.81, 0.99, 1.00, 1.15, 1.2) extend beyond the redshift limits of
existing optical and x-ray surveys, providing a unique sample for
probing the early era of cluster evolution.  Extensive ground-based and
HST  observations are already in hand and more are scheduled,  allowing
unprecedented  results to follow quickly from the ISO observations.