The assembly of cluster galaxies

Clusters of galaxies are the largest bound structures in the universe. As such, they represent an important tool for testing models of structure formation. In addition, because galaxies in clusters span a range of local environments and experience the full spectrum of galaxy evolution pathways, clusters are ideal targets for investigations of galaxy evolution. This dissertation utilizes observations of clusters to study both structure formation and galaxy evolution. In Chapter 1, we use Sloan Digital Sky Survey data of low redshift clusters to test the results of numerical simulations of structure growth in a ΛCDM universe. Considering that the simulations follow the non-linear process of structure formation over several orders of magnitude in mass, we found a remarkable agreement between theory and observation. In Chapters 2, 3, and 4 we present results from a Hubble Space Telescope survey of 10 high redshift (0.4 < z < 0.8) galaxy clusters from the ESO Distant Cluster Survey. These data, in conjunction with data on lower-redshift clusters, show that (1)the fraction of elliptical galaxies varies between 15% and 55% but shows no systematic trend with redshift; (2)the S0 fraction has systematically increased at the expense of the late-type fraction since z ∼ 0.8, strongly suggesting that late types have transformed into S0s within clusters; (3)the morphology-density relation is already in place at z≲0.8 ; and (4)most ellipticals in clusters were assembled at z≳3 , not in dissipationless mergers of galaxies containing old stellar populations at z < 1.