A multifaceted investigation of the resolved properties of galaxy mergers
| dc.contributor.author | Thorp, Mallory | |
| dc.contributor.supervisor | Ellison, Sara L. | |
| dc.date.accessioned | 2022-12-17T00:15:28Z | |
| dc.date.available | 2022-12-17T00:15:28Z | |
| dc.date.copyright | 2022 | en_US |
| dc.date.issued | 2022-12-16 | |
| dc.degree.department | Department of Physics and Astronomy | en_US |
| dc.degree.level | Doctor of Philosophy Ph.D. | en_US |
| dc.description.abstract | 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 inversely with signal-to-noise, to a degree that would make its application on IFS data highly problematic. I evaluate different methods to correct for the noise contribution to asymmetry at very low signal-to-noise, where previous studies have been unable to explore due to systematics, and present new algebraic corrections for noise and resolution to recover the intrinsic morphology measurements. I confirm these fit corrections can be applied to simulations with different physical models using the Illustris simulation, and provide estimations for the uncertainty on different correction methods at varying signal-to-noise and resolution regimes. This thesis also investigates how resolved molecular gas properties may impact the variety of ΔΣSFR behaviour in mergers. Spatially resolved measurements of CO emission are acquired using the Atacama Large Millimetre Array (ALMA) for 20 merging galaxies (either pairs or post-mergers) selected from the MaNGA survey. Eleven additional merging galaxies are selected from the ALMA MaNGA QUEnching and STar formation (ALMaQUEST) survey, resulting in a set of 31 mergers at various stages of interaction and covering a broad range of SFR. Combining resolved measurements of CO luminosity (from which molecular gas is derived) with MaNGA star formation rate maps provides insights on what drives merger-induced enhancements in star formation: an excess of molecular gas to fuel star formation, or a heightened efficiency in the rate at which gas is converted into stars. Using this data set I investigate galaxy-to-galaxy variations in key resolved scaling relations between star formation rate surface density, molecular gas surface density, and stellar mass surface density, revealing substantial diversity amongst mergers. Offsets in each resolved relation are quantified to determine if star formation rate, molecular gas fraction, and/or star formation efficiency (SFE) is enhanced in different regions of an individual galaxy. By comparing offsets in all three parameters I can discern whether gas fraction or SFE powers local enhancements in star formation rate. From this analysis I find merger-induced star formation can be driven by a variety of mechanisms, both within a galaxy and between different mergers, regardless of interaction stage. In closing remarks I highlight some exciting follow-up studies to this work: such as determining what causes mergers to have suppressed star formation, or how a merger-triggered active galactic nucleus might impact local star formation and gas properties. | en_US |
| dc.description.scholarlevel | Graduate | en_US |
| dc.identifier.uri | http://hdl.handle.net/1828/14565 | |
| dc.language | English | eng |
| dc.language.iso | en | en_US |
| dc.rights | Available to the World Wide Web | en_US |
| dc.subject | Astronomy | en_US |
| dc.subject | Galaxies | en_US |
| dc.subject | Galactic star formation | en_US |
| dc.subject | Galaxy interactions | en_US |
| dc.subject | Spatially resolved spectroscopy | en_US |
| dc.subject | Observational data analysis | en_US |
| dc.title | A multifaceted investigation of the resolved properties of galaxy mergers | en_US |
| dc.type | Thesis | en_US |