X-ray Detected Active Galactic Nuclei in Dwarf Galaxies at $0<z<1$

Abstract

We present a sample of accreting supermassive black holes (SMBHs) in dwarf galaxies at $z<1$. We identify dwarf galaxies in the NEWFIRM Medium Band Survey with stellar masses $M_{\star}<3\times 10^{9} M_{\odot}$ that have spectroscopic redshifts from the DEEP2 survey and lie within the region covered by deep (flux limit of $\sim 5\times 10^{-17} - 6\times 10^{-16} \rm{erg \ cm}^{-2} \ \rm{s}^{-1}$) archival Chandra X-ray data. From our sample of $605$ dwarf galaxies, $10$ exhibit X-ray emission consistent with that arising from AGN activity. If black hole mass scales roughly with stellar mass, then we expect that these AGN are powered by SMBHs with masses of $\sim 10^5-10^6 \ M_{\odot}$ and typical Eddington ratios $\sim 5\%$. Furthermore, we find an AGN fraction consistent with extrapolations of other searches of $\sim 0.6-3\%$ for $10^9 \ M_{\odot} \leq M_{\star} \leq 3\times 10^{9} \ M_{\odot}$ and $0.1<z<0.6$. Our AGN fraction is in good agreement with a semi-analytic model, suggesting that as we search larger volumes we may use comparisons between observed AGN fractions and models to understand seeding mechanisms in the early universe.