The resolved size and structure of hot dust in the immediate vicinity of AGN

¹ Max Planck Institute for Extraterrestrial Physics (MPE), Gießenbachstr. 1, 85748 Garching, Germany
e-mail: jdexter@mpe.mpg.de
² LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 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, UK
⁶ Department of Astrophysics and Atmospheric Sciences, Kyoto Sangyo University, Kyoto, Japan
⁷ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
⁸ School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
⁹ Department of Astronomy, The Ohio State University, Columbus OH, USA
¹⁰ Center for Cosmology and AstroParticle Physics, The Ohio State University, Columbus, OH, USA
¹¹ Space Telescope Science Institute, Baltimore, MD, USA
¹² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹³ Center for Computational Astrophysics, Flatiron Institute, 162 5th Ave., New York, NY 10010, USA
¹⁴ European Southern Observatory, Casilla 19001, Santiago 19, Chile
¹⁵ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
¹⁶ Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
¹⁷ Max Planck Institute for Radio Astronomy, Bonn, Germany
¹⁸ Universidade de Lisboa – Faculdade de Ciências, Campo Grande 1749-016, Lisboa, Portugal
¹⁹ Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
²⁰ CENTRA – Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal
²¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
²² Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
²³ JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309, USA
²⁴ Department of Particle Physics & Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel

Received: 23 September 2019
Accepted: 16 January 2020

Abstract

We use VLTI/GRAVITY near-infrared interferometry measurements of eight bright type 1 AGN to study the size and structure of hot dust that is heated by the central engine. We partially resolve each source, and report Gaussian full width at half-maximum sizes in the range 0.3−0.8 mas. In all but one object, we find no evidence for significant elongation or asymmetry (closure phases ≲1°). The narrow range of measured angular sizes is expected given the similar optical flux of our targets, and implies an increasing effective physical radius with bolometric luminosity, as found from previous reverberation and interferometry measurements. The measured sizes for Seyfert galaxies are systematically larger than for the two quasars in our sample when measured relative to the previously reported R ∼ L^1/2 relationship, which is explained by emission at the sublimation radius. This could be evidence of an evolving near-infrared emission region structure as a function of central luminosity.