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

TL;DR

This study confirms a tidal disruption event in an extremely low-mass galaxy in Abell 1795, providing insights into IMBH-hosting dwarf galaxies and their role in tidal disruption phenomena.

Contribution

Deep Gemini spectroscopy unambiguously identifies a low-mass galaxy hosting an IMBH and confirms the tidal disruption event as the flare's cause.

Findings

Host galaxy is extremely low-mass ($M_ullet ext{~} 10^{5.3-5.7} M_\odot$)

X-ray variability exceeds a factor of 10,000 over 15 years

Spectroscopy confirms the TDE origin over AGN activity

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 $(M_\ast\sim 3\times 10^8\; {\rm M}_{\odot})$ 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 $({\rm log}[M_{\bullet}/{\rm M}_{\odot}] \sim 5.3 - 5.7)$ 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.