Uncovering the Formation of Galaxies Using Their Stellar Populations

Abstract

The following thesis explores the stellar populations of Early Type galaxies, and in doing so develops a viable method by which to identify ex-situ stars in both spatially resolved and unresolved galaxies. Using simulated data from the EAGLE simulations, this thesis _rst lays a theoretical groundwork for the subsequent chapters by building predictions of ex-situ fraction in galaxies according to galaxy mass and size, as well as more readily observable properties such as surface brightness. Following this, the focus shifts to observational datasets of galaxies. The basics of a methodology with which to extract ex-situ fractions of galaxies is tested on MUSE data of NGC7135, _nding increases in ex-situ fraction with radius, in line with predictions from the EAGLE simulations. This methodology is improved upon and expanded in order to map the ex-situ populations present within 13 galaxies observed with MUSE. These are shown to display an increase in ex-situ fraction with mass and radius, with high gradients of increase in ex-situ material for the most massive and most extended galaxies. A similar methodology is _nally applied to a large statistically representative sample of spatially unresolved galaxies from the SDSS survey. This provides a lower galactocentric resolution view of the mass size plane but with a vastly improved sample size. With this study it is demonstrated that the smaller MUSE sample is a representative sample of galaxies and accurately demonstrates changes in ex-situ fraction with average galaxy mass and size. The results found in the chapters point to evidence of the `two-phase' scenario of galaxy formation, and present means to explore this further observationally.