Active Galactic Nuclei in Dwarf Galaxies

Abstract

Supermassive Black Holes (BHs; typically with masses greater than 10^5 solar masses) are ubiquitous in the cores of all massive galaxies (stellar masses greater than 10^10 solar masses). However, BHs in dwarf galaxies (stellar masses less than 10^9.5 solar masses) are more difficult to detect, and thus have remained relatively elusive. Theoretical work suggests that clues to BH formation and growth can be found in present day dwarf galaxies, making this an important population to study.

Searching for signs of BH accretion is one way of identifying BHs in dwarf galaxies more distant than the Local Group. Until recently, only a handful of dwarf galaxies had been identified with actively accreting central BHs, or Active Galactic Nuclei (AGNs). However, with the advent of large-scale surveys, it has been possible to search for signs of BH accretion in samples comprised of tens of thousands of galaxies. Recent works have identified roughly two hundred dwarf galaxies with AGN signatures, making it possible to begin to carry out demographic studies. This thesis describes an in-depth, multi-wavelength characterization of this relatively unexplored population. We determine which observational AGN identifiers used for massive galaxies also apply for dwarf galaxies, study the accretion properties of confirmed AGNs, and explore relationships between BH mass and host galaxy properties in these systems. We also present evidence for an active ~50, 000 solar mass BH in the center of the dwarf galaxy RGG 118, which at the time of writing, is the smallest BH yet reported in a galaxy center.