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

TL;DR

This study uses near-infrared interferometry to measure the size and structure of hot dust around 8 bright AGN, revealing size-luminosity relations and potential structural evolution with luminosity.

Contribution

First direct interferometric measurements of hot dust sizes in multiple AGN, showing size-luminosity scaling and structural differences between Seyferts and quasars.

Findings

Measured Gaussian FWHM sizes of 0.3-0.8 mas.

No significant elongation or asymmetry detected.

Sizes increase with bolometric luminosity, consistent with sublimation radius expectations.

Abstract

We use VLTI/GRAVITY near-infrared interferometry measurements of 8 bright, Type 1 AGN to study the size and structure of hot dust heated by the central engine. We partially resolve each source, and report Gaussian FWHM sizes in the range 0.3-0.8 milliarcseconds. In all but one object, we find no evidence for significant elongation or asymmetry (closure phases < 1 deg). The effective physical radius increases with bolometric luminosity as found from past 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 explained by emission at the sublimation radius. This could be evidence of evolving near-infrared emission region structure as a function of central luminosity.