AAS 207th Meeting, 8-12 January 2006
Session 190 Galaxy Clusters at z $>$ 0.5
Oral, Thursday, 10:00-11:30am, January 12, 2006, Maryland

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[190.07] Evolution of the color-magnitude relation at z~1

S. Mei, J. B. Blakeslee, R. Demarco, H. Ford, N. Homeier (Johns Hopkins University), B.P. Holden, G.D. Illingworth (Lick Observatory), M. Franx (Leiden Observatory), M. Postman (Space Telescope Science Institute), P. Rosati, A. Rettura, V. Strazzullo (European Southern Observatory), ACS IDT Team

HST permits the study of high--z cluster galaxies in unprecedented detail and offers a unique opportunity to examine the processes driving galaxy evolution. As part of our Advanced Camera for Surveys (ACS) intermediate redshift cluster survey, we have observed 8 galaxy clusters with redshift between 0.8 and 1.3. At these redshifts, galaxy clusters are still assembling and galaxies are evolving towards the populations that we observe today. Recent results from the ACS cluster survey have shown that galaxy clusters at redshift around unity show differences but also many similarities with local clusters, in terms of galaxy populations and their distribution. One of the most striking similarities is that the tight relation between galaxy colors and luminosities that applies to local early-type galaxies (the color-magnitude relation; CMR) is already in place at redshifts as high as z~1.3. The precise measurement of the scatter around the CMRs of our cluster sample permits us to constrain the formation ages of the redder early-type population to be at z>2.5. We will present our most recent results and discuss them as a function of cluster properties at z~1.

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