Environmental Impacts on Simulated Galaxy Properties

Abstract

Galaxies in the Universe come in a variety of shapes, sizes, and colors. The range of properties is produced from a combination of physical processes. Galaxies live within various structures and therefore receive different influences from their environment that alter their evolutionary pathways. Thus, not only does each physical process need to be understood, but we also need to understand the interactions of these processes with each other and with the environment in which they live. In this thesis, I work towards a more complete picture of galaxy evolution by studying how galaxies are affected by the environment in which they evolve. I use cosmological and zoom-in simulations to study the components of galaxies and how they relate to each other. I start with a study on measuring the boundaries of halos. In order to study galaxies, their dark matter halo, and the environment in which they live, it is integral to have a robust size measurement of these objects. Using massive galaxy groups and clusters in the IllustrisTNG simulations, I show how the splashback radius, which defines a halo’s boundary by separating orbiting material from infalling material, varies depending on the measurement method. I then show how selection effects can bias measurements of the splashback radius by examining various populations of galaxies. The more massive and brighter a galaxy is, the more it deviates from the dark matter distribution. This is significant since these are the galaxies that are most easily observed. Motivated by uncovering the underlying cause of galaxy population bias, I present a study of how galaxy properties change with time spent in the cluster. I demonstrate that certain scaling relations, in particular the stellar-to-halo mass ratio, the stellar size, and the metallicity as functions of stellar mass, systematically deviate from the standard relation for galaxies that have spent more time in their cluster. I also show that measurements of the splashback radius stabilize after approximately 5 Gyrs, the time it takes for one pass through the cluster. Finally, I run a new suite of zoom-in simulations introducing a new model for self-interacting dark matter that includes a significant amount of elastic, exothermic, and endothermic scattering. This is the first time that a model emphasizing endothermic scattering has been simulated in a galactic environment. I show that this model can produce realistic halos and has the potential to mitigate several of the existing discrepancies between observations of galaxies and simulations of cold dark matter.