Searching for signatures of accreting massive black holes in dwarf galaxies

Abstract

Identifying and analyzing massive black holes (BHs) in dwarf galaxies can advance our understanding of the formation and development of supermassive BHs. Searching for these objects can prove troublesome, however. Massive BHs, with masses of M BH < or ~ 10 6 M circled dot, are smaller than their supermassive cousins (M BH ? 10 6-10 9 M circled dot), and the dwarf galaxies they reside in can yield very different environments than what one might find in a more standard massive galaxy, resulting in a different set of challenges than searching out active galactic nuclei (AGN) powered by supermassive BHs. Here we describe several methods for both identifying AGN candidates powered by massive BHs and searching for evidence to confirm the presence or absence of AGN candidates in dwarf galaxies. For the latter, we use different combinations of radio, X-ray, and mid-IR observations to search for AGN signatures, elucidating the various benefits and difficulties that lie with each one, and reporting the results when applied to our varying samples. For the former, we analyze the efficacy of a mid-IR color-color AGN selection method when applied to dwarf galaxies instead of massive galaxies, and use X-ray observations from a newly-released catalog to search for new AGN candidates in dwarf galaxies.