Galaxy clusters are the most-massive, collapsed, galaxy environments in the Universe, and they exist along a spectrum of dynamical state and virialization. Such extreme environments extend the range of physical processes that we can study relevant to galaxy evolution. Therefore, galaxy clusters are important laboratories to advance our understanding of galaxy evolution. With optical and X-ray observations, along with dark matter only simulations, we test methods for classifying galaxy cluster dynamical state. We show that the shape of the member-galaxy redshift distribution, for a given cluster, is a useful proxy for cluster dynamical state which correlates with cluster X-ray morphology. Applying these classifications to simulated clusters, we show that unrelaxed clusters have experienced recent major mergers as well as active accretion of new galaxies. We also present evidence for enhanced star formation in galaxies within unrelaxed clusters, compared to counterparts in relaxed systems. This trend is likely connected to the shorter times-since-infall for galaxies in unrelaxed clusters. Interactions between galaxies and the intracluster medium (ICM) play an important role in quenching galaxy star formation. With a sample of SDSS clusters, and archival X-ray observations from the Chandra observatory, we investigate galaxy star formation as a function of ICM density. For all masses, the quenched fraction of galaxies increases with ICM density. For low-mass galaxies, there is evidence for enhanced quenching in the densest cluster regions, consistent with ram pressure stripping. To further probe ram pressure in clusters, we use high-resolution imaging to search for galaxies undergoing stripping in the Coma cluster. We present ~40 ram pressure stripping candidates, which are consistent with being stripped on their first infall toward the Coma centre. These galaxies show enhanced star formation rates, suggesting that gas compression from ram pressure may be catalyzing star formation. Environmentally-driven quenching in galaxy clusters is a function of both, both how long a galaxy has been part of a cluster, and how efficiently cluster processes quench galaxies. The former is informed by accurate characterization of cluster dynamical state, and the latter by detailed studies of quenching mechanisms as a function of galaxy mass, both of which are focal points of this work.

Doctor of Philosophy (PhD)

Thesis