Tidal Disruption Event Host Galaxies in the Context of the Local Galaxy Population

Abstract

Abstract We study the properties of tidal disruption event (TDE) host galaxies in the context of a catalog of ∼500,000 galaxies from the Sloan Digital Sky Survey. We explore whether selection effects can account for the overrepresentation of TDEs in E+A/post-starburst galaxies by creating matched galaxy samples. Accounting for possible selection effects due to black hole (BH) mass, redshift completeness, strong active galactic nucleus presence, bulge colors, and surface brightness can reduce the apparent overrepresentation of TDEs in E+A host galaxies by a factor of ∼4 (from ∼×100–190 to ∼×25–48), but cannot fully explain the preference. We find that TDE host galaxies have atypical photometric properties compared to similar, “typical” galaxies. In particular, TDE host galaxies tend to live in or near the “green valley” between star-forming and passive galaxies, and have bluer bulge colors ( Δ ( g − r ) ≈ 0.3 mag), lower half-light surface brightnesses (by ∼1 mag/arcsec2), higher Sérsic indices ( Δ n g ≈ 3 ), and higher bulge-to-total-light ratios ( Δ B / T ≈ 0.5 ) than galaxies with matched BH masses. We find that TDE host galaxies appear more centrally concentrated and that all have high galaxy Sérsic indices and B/T fractions—on average in the top 10% of galaxies of the same BH mass—suggesting a higher nuclear stellar density. We identify a region in the Sérsic index and BH mass parameter space that contains ∼2% of our reference catalog galaxies but ≥ 60 % of TDE host galaxies. The unique photometric properties of TDE host galaxies may be useful for selecting candidate TDEs for spectroscopic follow-up observations in large transient surveys.