Toward measuring supermassive black hole masses with interferometric observations of the dust continuum^⋆

¹ Max Planck Institute for Extraterrestrial Physics (MPE), Giessenbachstr.1, 85748 Garching, Germany
² LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 Place Jules Janssen, 92195 Meudon, France
³ I. Institute of Physics, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
⁴ Departments of Physics and Astronomy, Le Conte Hall, University of California, Berkeley, CA 94720, USA
⁵ Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
⁶ Department of Astrophysics & Atmospheric Sciences, Kyoto Sangyo University, Kamigamo-motoyama, Kita-ku, Kyoto 603-8555, Japan
⁷ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Boulevard de l’Observatoire, 06304 Nice Cedex 4, France
⁸ School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
⁹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁰ Center for Computational Astrophysics, Flatiron Institute, 162 5th Ave., New York, NY 10010, USA
¹¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile
¹² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
¹³ Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA, Leiden, The Netherlands
¹⁴ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
¹⁵ Universidade de Lisboa – Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
¹⁶ Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
¹⁷ CENTRA – Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal
¹⁸ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁹ Instituto de Astrofísica de Canarias (IAC), E-38205 La Laguna, Tenerife, Spain
²⁰ Department of Astrophysical & Planetary Sciences, JILA, University of Colorado, Duane Physics Bldg., 2000 Colorado Ave., Boulder, CO 80309, USA
²¹ Research School of Astronomy and Astrophysics, Australian National University, Bart Bok Rd, Canberra, ACT 2611, Australia
²² Retired – c/o T.L. Turner, 205 South Prospect Street, Granville, OH 43023, USA

Received: 1 August 2022
Accepted: 28 September 2022

Abstract

This work focuses on active galactic nuclei (AGNs) and on the relation between the sizes of the hot dust continuum and the broad-line region (BLR). We find that the continuum size measured using optical/near-infrared interferometry (OI) is roughly twice that measured by reverberation mapping (RM). Both OI and RM continuum sizes show a tight relation with the Hβ BLR size, with only an intrinsic scatter of 0.25 dex. The masses of supermassive black holes (BHs) can hence simply be derived from a dust size in combination with a broad line width and virial factor. Since the primary uncertainty of these BH masses comes from the virial factor, the accuracy of the continuum-based BH masses is close to those based on the RM measurement of the broad emission line. Moreover, the necessary continuum measurements can be obtained on a much shorter timescale than those required monitoring for RM, and they are also more time efficient than those needed to resolve the BLR with OI. The primary goal of this work is to demonstrate a measuring of the BH mass based on the dust-continuum size with our first calibration of the R_BLR–R_d relation. The current limitation and caveats are discussed in detail. Future GRAVITY observations are expected to improve the continuum-based method and have the potential of measuring BH masses for a large sample of AGNs in the low-redshift Universe.