An enhanced rate of tidal disruptions in the centrally overdense E+A galaxy NGC 3156

Abstract

Time domain optical surveys have discovered roughly a dozen candidate stellar tidal disruption flares in the last five years, and future surveys like the {\it Large Synoptic Survey Telescope} will likely find hundreds to thousands more. These tidal disruption events (TDEs) present an interesting puzzle: a majority of the current TDE sample is hosted by rare post-starburst galaxies, and tens of percent are hosted in even rarer E+A galaxies, which make up $\sim 0.1\%$ of all galaxies in the local universe. E+As are therefore overrepresented among TDE hosts by 1-2 orders of magnitude, a discrepancy unlikely to be accounted for by selection effects. We analyze {\it Hubble Space Telescope} photometry of one of the nearest E+A galaxies, NGC~3156, to estimate the rate of stellar tidal disruption produced as two-body relaxation diffuses stars onto orbits in the loss cone of the central supermassive black hole. The rate of TDEs produced by two-body relaxation in NGC~3156 is large when compared to other galaxies with similar black hole mass: $\dot{N}_{\rm TDE}\sim 1\times 10^{-3}~{\rm yr}^{-1}$. This suggests that the preference of TDEs for E+A hosts may be due to central stellar overdensities produced in recent starbursts.