Galaxy Evolution and Environment

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The formation and evolution of galaxies is intimately tied to the environment and large scale structure in which they reside. Galaxy groups and clusters provide a unique laboratory to study the effects of a range of environments, up to that of the densest in the universe, on galaxy evolution and the history of star formation. The study of cluster evolution, including the galaxy population, cluster morphology, mergers, cluster mass function and the build-up of the giant central galaxy (called Brightest Cluster Galaxy, or BGC) informs many issues directly related to both galaxy formation and evolution, the growth of large-scale structure, and cosmology. My proposal will be based on three large surveys of clusters designed to optimize the study of clusters at redshift (z) greater than 1 (or, when the universe was less than half of its current age). The two surveys already completed their data acquisition and reduction are: the SpARCS (Spitzer Adaptation of the Red-Sequence Cluster Survey) survey, which uses infrared imaging from the Spitzer Space Telescope combined with optical imaging from ground-based telescopes to produce a catalog of over 200 clusters at z>1; and GCLASS (Gemini Cluster Astrophysical Science Survey), which obtained spectra for over 400 cluster galaxies in 9 of the riches clusters from SpARCS at z~1. The third is the on-going GoGreen Project (Gemini Observations of Galaxies in Early Rich Environments), an approved large program at the Gemini Observatory, which will obtain spectra for ~1000 cluster members in 21 galaxy clusters and groups at z>1. One key scientific goal of my proposal is to use these large spectroscopic and photometric catalogs to explore the time scale of the suppression of star formation in galaxies in-falling into groups and clusters. This will be done by examining various star-formation indicators for galaxies in different locations of the clusters. Another main project is to investigate the frequency and types of merging galaxies in clusters and different galaxy density regions, allowing us to gain insights into the contribution of mergers to both inducing and the quenching of star formation. I will also use the very extensive cluster and galaxy catalogs to investigate the shape of galaxy clusters as a function of epoch and probe the connections between the morphology of galaxy clusters to cluster evolution and the cluster galaxy population, comparing these results with simulations. The goal is to investigate how cluster morphology correlates with the mass build-up of clusters and stellar contents of clusters.