Mass Loss and Preprocessing of Galaxies Traversing Group Environments

Abstract

Groups and clusters of galaxies are environments that can significantly influence the evolution of galaxies within them. On average, as galaxies are accreted onto these structures, blue, spiral, star-forming galaxies are transformed into red, elliptical, quiescent galaxies. A number of physical environmental processes can affect the various components of galaxies and each process leaves a signature on their dark matter, gas and stellar content. Additionally, a natural result of the hierarchical growth of structure in the Universe is that more massive clusters accrete smaller groups of galaxies, which may already have exerted an environmental influence on their members. These galaxies may therefore be preprocessed in smaller groups before their final accretion. The implication of preprocessing is that some of the environmental effects attributed to clusters may in fact be established in the group environment.

In this thesis, we concentrate on the final masses and mass loss experienced by galaxies in dense environments and the degree to which they are preprocessed. Using galaxy analogues in a dark matter simulation, we investigate the phenomena of mass segregation and mass loss occurring in groups and clusters and find that tidal effects dominate their halo mass evolution. A large fraction of these galaxy analogues are preprocessed, resulting a large proportion of their total mass loss occurring \emph{before} they are accreted by their final host haloes. We also conduct a high-resolution hydrodynamical simulation of a galaxy group to study the detailed mass loss of individual galaxies in dark matter, gas and stars. We find, again, that tidal stripping dominates the mass loss experienced by these galaxies and that it removes large amounts of dark matter and diffuse gas, while leaving most of their stellar content intact. This differential mass loss results in these galaxies having significantly different stellar mass-to-halo mass (SMHM) relations compared to field galaxies or galaxies that were accreted individually. This work stresses the important role preprocessing plays in galaxy evolution within dense environments and emphasizes the challenges of using galaxy observations containing mixed populations to constrain the effects of evolutionary mechanisms.