2018ApJ...853...39G

The rate of tidal disruption events (TDEs), R_TDE, is predicted to depend on stellar conditions near the super-massive black hole (SMBH), which are on difficult-to-measure sub-parsec scales. We test whether R_TDE depends on kpc-scale global galaxy properties, which are observable. We concentrate on stellar surface mass density, Σ_M*_, and velocity dispersion, σ_v, which correlate with the stellar density and velocity dispersion of the stars around the SMBH. We consider 35 TDE candidates, with and without known X-ray emission. The hosts range from star-forming to quiescent to quiescent with strong Balmer absorption lines. The last (often with post-starburst spectra) are overrepresented in our sample by a factor of 35_–17⁺²¹ or 18_–7⁺⁸, depending on the strength of the Hδ absorption line. For a subsample of hosts with homogeneous measurements, Σ_M*₌₁₀9^–1010^M☉_/kpc², higher on average than for a volume-weighted control sample of Sloan Digital Sky Survey galaxies with similar redshifts and stellar masses. This is because (1) most of the TDE hosts here are quiescent galaxies, which tend to have higher Σ_M*_ than the star-forming galaxies that dominate the control, and (2) the star-forming hosts have higher average Σ_M*_ than the star-forming control. There is also a weak suggestion that TDE hosts have lower σ_v than for the quiescent control. Assuming that R_TDE∝Σ_M*_^α^×σ_v^β^, and applying a statistical model to the TDE hosts and control sample, we estimate 1=0.9±0.2 and 1=-1.0±0.6. This is broadly consistent with R_TDE being tied to the dynamical relaxation of stars surrounding the SMBH.