Thinking outside the halo: a semi-analytic approach to galaxies and their environments

This thesis addresses two questions fundamental to galaxy formation: how does a galaxy's environment affect its evolution and how does a galaxy's evolution affect its environment. To answer these questions, this thesis uses semi-analytic models to explore the co-evolution of galaxies and their environs. First, it compares commonly used environment metrics to better understand how proto-clusters in the early universe become the giant galaxy clusters we see nearby. Second, it develops the definition of environment to include not only nearby galaxies but also the intergalactic medium. And finally, it builds a model of co-evolving galaxies and the surrounding intergalactic medium.