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 × 105 M⊙ ≤ MBH ≤ 2 × 107 M⊙. The TDE host galaxy sample is dominated by low-mass black holes (~ 106 M⊙), as expected from theoretical predictions. The blackbody peak luminosity of TDEs with MBH =≤107.1 M⊙ is consistent with the Eddington limit of the supermassive black hole (SMBH), whereas the two TDEs with MBH ≥ 107.1 M⊙ have peak luminosities below their SMBH Eddington luminosity, in line with the theoretical expectation that the fallback rate for MBH ≥ 107.1 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 106 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.
Bibliographical noteFunding Information:
We would like to thank the anonymous referee for suggestions that improved the manuscript. TW wishes to thank D. Lena for assisting in the observing runs and is grateful to D. Lena and M. Torres for useful discussions. SvV is supported by NASA through a Hubble Fellowship (HSTHF2-51350). PGJ acknowledges support from European Research Council Consolidator Grant 647208. NCS acknowledges support through NASA from Einstein Postdoctoral Fellowship Award Number PF5-160145. The research leading to these results has received funding from the European Union's Horizon 2020 Programme under the AHEAD project (grant agreement no. 654215). SG is supported in part by NSF CAREER grant 1454816 and NASA Keck Grant 1568615. Part of this work was inspired by discussions within International Team #371 Using Tidal Disruption Events to Study Super-Massive Black Holes at the International Space Science Institute in Bern, Switzerland. We thank Tom Marsh for developing the software package MOLLY. TheWHT is operated on the island of La Palma by the Isaac Newton Group of Telescopes in the SpanishObservatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias. The ISIS spectroscopy was obtained as part of programmes W15BN010 and W16AN007. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory with the director's discretionary time, programme ID 297.B-5062(A) (P. I. Jonker). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of theW. M. Keck Foundation. We wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community.We are most fortunate to have the opportunity to conduct observations from this mountain.
© 2017 The Authors.
- Accretion discs
- Galaxies: bulges
- Galaxies: fundamental parameters
- Galaxies: kinematics and dynamics
- Galaxies: nuclei