Structural Decomposition of Merger-Free Galaxies Hosting Luminous AGN

Fahey, Matt and Simmons, Brooke (2023) Structural Decomposition of Merger-Free Galaxies Hosting Luminous AGN. Masters thesis, Lancaster University.

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Abstract

Black hole-galaxy co-evolution is a cornerstone of modern extragalac- tic astrophysics. Previous work has suggested galaxy mergers are the primary mechanism through which co-evolution occurs, growing the mass of both galaxies and their black holes. More recent ob- servational studies have called this concept into question, proposing merger free pathways for black hole-galaxy co-evolution. We investi- gate a sample of disk-dominated galaxies hosting luminous AGN and structurally decompose them using GALFIT to reveal their morpho- logical components. We detect a classical bulge component in 53.3 ± 0.5% of the galaxies in our sample, however we find these galaxies are still unambiguously disk-dominated, with an average B/Tot for the entire sample of 0.1 ± 0.1. We find galaxies hosting only bulges host overly massive black holes and more luminous AGN in comparison to galaxies hosting only pseudobulges, though we also find evidence that mergers are not a requirement to grow black holes to supermas- sive size. We investigate the barred fraction of our sample and find that galaxies hosting bars host neither overly massive black holes, nor overly luminous AGN, suggesting the presence of a bar is not a requirement to grow black holes to supermassive size in the local Universe in the absence of major mergers. Considering black hole- galaxy mass relations we find some correlation between bulge mass and black hole mass for disk-dominated galaxies, though we note that this correlation is significantly weaker in comparison to the relation for bulge-dominated galaxies. Furthermore, a significant fraction (≳ 90%) of these black holes are overly massive when compared to this canonical relation. We find a similar correlation between total stel- lar mass and black hole mass for the disk-dominated galaxies, and investigate the extent to which these findings indicate differences in the stochasticity of black hole-galaxy co-evolution in disk-dominated versus bulge-dominated systems.