UCLA

Supermassive black holes (SMBHs) are thought to co-evolve alongside their host galaxiesboth through mergers with other SMBHs, and through accretion and the active galactic nucleus (AGN) emission it powers. Binary SMBHs are a step along the way to SMBH mergers, and so are important for understanding SMBH-galaxy co-evolution. Understanding the activity period of AGN (the AGN duty cycle) is also important for understanding how much of an impact AGN can have on their host galaxies. It is for these reasons in my thesis that I studied binary SMBHs and the AGN duty cycle. In my thesis I investigated whether candidate binary SMBHs had distinct spectra from single SMBHs, a phenomenon predicted by many theoretical models. I found that they do not, which could mean that the theoretical models are incorrect, or that the candidates were not truly binary SMBHs. This null result motivates additional theory development as well as future observational campaigns to find or confirm binary SMBHs. I also searched for recently deactivated AGN in a sample of obscured AGN, to see if that could shed light on the time periods over which AGN turn off and on. I found one AGN that deactivated no more than 87-220 years ago, indicating that perhaps AGN flicker on timescales of decades and centuries.