Galaxy Evolution in Clusters: Exploring the Role of Ram Pressure Stripping Using Simulations

Galaxies entering clusters are affected spectroscopically and morphologically by the change in their environment. The cluster population has evolved from z∼0.5 to z=0, both in color (the Butcher-Oemler effect), and in morphology (spirals to S0s).;In this thesis, we study galaxy evolution in clusters, focusing on gas removal as a key step in both spectroscopic and morphological evolution. We use both cosmological and idealized simulations, and compare our results to observations.;We begin by using a cosmological simulation to examine the evolution of cluster galaxies in a cluster with rvir = 1.8 Mpc. We follow a large number of galaxies and track each galaxy's gas and stellar mass changes to discover what mechanism(s) dominate their evolution. We find that while gas is lost due to a variety of mechanisms, the most common way is via a gas-only stripping event, and the amount of gas lost correlates with the ram pressure the galaxy is experiencing. The timescale for complete gas removal is ≥ 1 Gyr.;Although this gas-stripping occurs primarily in the central region (< 1 Mpc), it can affect galaxies out to the virial radius of the cluster (1.8 Mpc). This is because the ram pressure a galaxy experiences at a fixed distance from the cluster center can vary by well over an order of magnitude. We find that this variation in ram pressure is due in almost equal parts to variation in the intracluster medium (ICM) density and in the relative velocity between the galaxy and the ICM.;Observations showing populations of cluster galaxies that are rarely found in the field, such as passive spirals, are clues to the processes at work in the cluster environment. Galaxies in the midst of strong interactions show clear indications of which mechanism is affecting them.;We then perform high resolution (38 pc) simulations of a galaxy undergoing ram pressure stripping, first investigating the properties of the remaining gas disk. We self-consistently produce the clumpy, multiphase ISM by including radiative cooling. Gas in multiphase galaxies is stripped more quickly and to a smaller radius than gas in galaxies without radiative cooling because the multiphase medium naturally includes high density clouds set inside regions of lower density. Ram pressure quickly strips low density gas from a range of galactic radii, and higher density clouds can then be ablated. Low ram pressure compresses gas into high density clouds, while high ram pressure leads to a smaller amount of high-density gas.;Focusing on the gas properties in the stripped tail, we find that including cooling results in a highly structured tail, with a wider range of temperatures and densities. The tail is significantly narrower in runs with radiative cooling, in agreement with observed wakes. In addition, we make predictions of H I, Halpha and X-ray emission from the wake, showing that we generally expect detectable H I and Halpha.;After running simulations with differing ICM conditions, we find that the primary requirement for the production of X-ray bright tails is a high pressure ICM. This is because the stripped tail is mostly in pressure equilibrium with the ICM, but mixing leaves it with densities and temperatures intermediate between the cold gas in the disk and the hot ICM. Given a high ICM pressure, this mixed gas lies in the X-ray bright region of the phase diagram. We compare these simulations to observations of the ram pressure stripped tail of ESO 137-001 to constrain the level of mixing and efficiency of heat conduction in the ICM.;We then consider the effects of varying the strength of ram pressure on the galaxy disk and stripping profile. We find that the amount of mass loss depends both on the peak ram pressure and the total column density of gas through which the galaxy has passed. No net fallback of stripped gas occurs while ram pressure is increasing or constant. Net fallback onto the disk does not occur until ∼375 Myr after the peak ram pressure in our varying wind case.