Abstracts Astronomy & Space Science

A multifaceted investigation of the resolved properties of galaxy mergers

by Mallory Thorp

One promising mechanism to understand the impressive diversity of galaxies observed today, and how galaxies may transition between different populations, is galactic mergers. Interactions between galaxies of comparable masses can dramatically alter the morphology, chemical composition, star formation activity, and central blackhole accretion of their constituents. Although the impacts of galaxy interactions can be seen at relatively early stages of an encounter, the entire process from first approach to coalescence takes hundreds of millions of years. Consequently, observations of galaxies at different stages of an interaction are required to reconstruct the complete merging process. Such an investigation requires large spectroscopic galaxy surveys to probe a variety of merger stages, which until recently were limited to global properties. The advent of large integral field spectroscopy (IFS) surveys has provided the novel opportunity to examine changes induced by a merger on a kpc-scale. This thesis presents the largest IFS analysis of galaxy mergers to date using the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. From 10,000 MaNGA galaxies I visually classify 400 post-merger galaxies, and with the aid of spectroscopic pair catalogues identify 1523 interacting pairs. The global and resolved star formation rate (SFR) properties of the merger sample have significant overlap with the non-interacting galaxies, though post-mergers tend to have slightly higher star formation rate and stellar mass surface densities. Enhancements and deficits in star formation (ΔΣSFR) and metallicity (ΔO/H) are determined for every spatial pixel containing a spectrum (spaxel) based on well established scaling relationships with stellar mass surface density; these are subsequently compressed into 2-dimensional radial profiles to investigate how the impact of an interaction varies with radius. Radial profiles reveal how a centralized starburst in mergers depends on interaction stage, global SFR enhancement, and the ratio of interacting galaxy masses. Though average trends arise, such as post-mergers and galaxies with larger or comparable mass companions having the strongest central starburst and metallicity dilution, I uncover considerable variation in ΔΣSFR and ΔO/H profiles in mergers. In an effort to expose spatially resolved changes concealed in azimuthally averaged radial profiles, I propose adopting non-parametric morphology metrics asymmetry and concentration for IFS data products as an alternative analysis tool. In this thesis I utilize galaxies from the IllustrisTNG simulation to assess the applicability of concentration and asymmetry indicators to the stellar mass distribution in galaxies. Specifically, I test whether the intrinsic values of concentration and asymmetry (measured directly from the simulation stellar mass particle maps) are recovered after the application of measurement uncertainty and varying resolution. I find random noise has a non-negligible systematic effect on asymmetry that scales…