Deep Spectroscopy of the $M_V\sim -14.8$ Host Galaxy of a Tidal Disruption Flare in A1795

Abstract

A likely tidal disruption of a star by the intermediate-mass black hole (IMBH) of a dwarf galaxy was recently identified in association with Abell 1795. Without deep spectroscopy for this very faint object, however, the possibility of a more massive background galaxy or even a disk-instability flare from a weak AGN could not be dismissed. We have now obtained 8 hours of Gemini spectroscopy which unambiguously demonstrate that the host galaxy is indeed an extremely low-mass $(M_{\ast }\sim 3\times 10^8{\mathrm{M}}_{\odot })$ galaxy in Abell 1795, comparable to the least-massive galaxies determined to host IMBHs via other studies. We find that the spectrum is consistent with the X-ray flare being due to a tidal disruption event rather than an AGN flare. We also set improved limits on the black hole mass $(\log [M_{\bullet }/{\mathrm{M}}_{\odot }]\sim 5.3-5.7)$ and infer a 15-year X-ray variability of a factor of $>10^4$. The confirmation of this galaxy-black hole system provides a glimpse into a population of galaxies that is otherwise difficult to study, due to the galaxies' low masses and intrinsic faintness, but which may be important contributors to the tidal disruption rate.

9 pages, 4 figures. Accepted by MNRAS

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