Dissecting Merging Galaxies Using Integral Field Spectroscopy

Abstract

Galaxies grow through the accretion of gas, minor mergers and major mergers in the hierarchical picture of galaxy evolution. The merging of two gas-rich galaxies cause gas to be driven towards the centres of the individual galaxies producing intense circum-nuclear star formation and creating a fuel reservoir for the accretion onto the central blackhole. Feedback due to supernova winds or AGN (Active Galactic Nuclei) accretion blows out the surrounding gas through an outflow at later merger stages, that may be large enough to deplete the galaxies of their fuel reservoir and hence shut down star formation and starve the central black hole. It is still uncertain what the impact of outflows is on merging galaxies, and when in the merging process they are most significant. This thesis has used Integral Field Spectroscopy (IFS) observations of merging galaxies to probe the impact of outflows on gas-rich major mergers. Using velocity-resolved absorption and emission lines arising from the interstellar medium of the galaxies, this thesis shows that the occurrence of outflows increases with merger stage and also that these outflows are not caused by the same physical processes, such as star formation or an AGN, in each merger system. This thesis describes the machine learning algorithm created to expedite the decision making process of multi-component emission line fitting for studies of ionised gas in large IFS surveys. The remainder of the research outlined in this thesis has identified a number of new facts about merging galaxies that are important for further research in this field including the following; Composite galaxies are being incorrectly classed as the same type of galaxy when they can range in excitation mechanisms; Composite galaxies are not the same between different morphologies, including between merging galaxies and isolated galaxies; The outflow from the northern nucleus of the merging system IRAS F10257- 4339 can be traced in neutral, ionised, and molecular gas, and is most likely caused by starformation; Outflows of neutral gas from galaxies increases with merger stage.