Black hole masses of tidal disruption event host galaxies

Abstract

The mass of the central black hole in a galaxy that hosted a tidal disruption event (TDE) is an important parameter in understanding its energetics and dynamics. We present the first homogeneously measured black hole masses of a complete sample of 12 optically/UV-selected TDE host galaxies (down to ghost ≤ 22 mag and z = 0.37) in the Northern sky. The mass estimates are based on velocity dispersion measurements, performed on late time optical spectroscopic observations. We find black hole masses in the range of 3 × 10^5 M_⊙ ≤ M_(BH) ≤ 2 × 10^7 M_⊙. The TDE host galaxy sample is dominated by low-mass black holes (∼ 10^6 M_⊙), as expected from theoretical predictions. The blackbody peak luminosity of TDEs with M_(BH) ≤ 10^(7.1) M_⊙ is consistent with the Eddington limit of the supermassive black hole (SMBH), whereas the two TDEs with M_(BH) ≥ 10^(7.1) M_⊙ have peak luminosities below their SMBH Eddington luminosity, in line with the theoretical expectation that the fallback rate for M_(BH) ≥ 10^(7.1) M_⊙ is sub-Eddington. In addition, our observations suggest that TDEs around lower mass black holes evolve faster. These findings corroborate the standard TDE picture in 10^6 M_⊙ black holes. Our results imply an increased tension between observational and theoretical TDE rates. By comparing the blackbody emission radius with theoretical predictions, we conclude that the optical/UV emission is produced in a region consistent with the stream self-intersection radius of shallow encounters, ruling out a compact accretion disc as the direct origin of the blackbody radiation at peak brightness.

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