Early-type galaxies in clusters are some of the oldest and most massive galaxies in the universe. We know this from measurements of their colors and their mass to light ratios. They also dominate the massive end of the cluster galaxy population. My recent work has focused on the evolution in the numbers of these objects in massive clusters. We find that the early-type galaxy fraction does not change for galaxies with stellar masses above log M = 10.6. Previous works finds that the early-type galaxy fraction evolves rapidly, but most of that evolution must be occuring in lower mass systems. My most current project is investigating if the fraction of S0 galaxies, disk-like systems that are hypothesized to come from spiral galaxies that have stopped forming new stars, evolves in mass-selected samples.

The ACS team has constructed a sample of z=0.8 to 1.3 clusters of galaxies. For each cluster, we have imaging in two passbands to study galaxy properties as a function of morphology, color and stellar mass. Below I list some of the papers, only those from 2006.

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