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B. P. Holden, S. A. Stanford (UC, Davis), P. von Dokkum (CIT), P. Eisenhardt (JPL), M. Dickinson (STScI)
We have constructed a sample of eleven z>0.6 clusters of galaxies with a combination of deep near-infrared imaging and archival HST data. With this sample, we have measured the evolution in the cluster early-type galaxy population at a redshift regime where the mass assembly of those galaxies should be occurring.
In agreement with previous results, we have found that the slopes of the color-magnitude relation shows no statistically significant deviation from a passive evolution prediction on a cluster by cluster basis. However, the population of all z>0.9 clusters of galaxies have slopes flatter than expected from passive evolution, a prediction of the merger formation scenario.
Overall, we find that the stellar populations of early-type galaxies are consistent with a formation epoch of 2 < z < 3. This agrees with many other studies of cluster populations.
Finally, we will discuss our studies of the morphology of early-type galaxies using projections of the fundamental plane. Such scaling relations will allow us new insights into the evolution of early-type galaxies at these redshifts.