The complexity of parsec-scaled dusty tori in AGN

TL;DR

This paper investigates the complex, parsec-scale dusty tori in AGN, revealing significant structural differences and challenging the notion of a uniform dusty doughnut in all active galactic nuclei, based on interferometric observations.

Contribution

It provides detailed interferometric analysis of the dust distribution in the Circinus galaxy, highlighting its dense, disk-like core and surrounding warm dust structures, and questions the uniformity of AGN tori.

Findings

Dust emission originates from a dense, disk-like structure.

Significant warm dust exists within the ionisation cone.

Large scatter in size-luminosity relation indicates diverse dust tori.

Abstract

Warm gas and dust surround the innermost regions of active galactic nuclei (AGN). They provide the material for accretion onto the super-massive black hole and they are held responsible for the orientation-dependent obscuration of the central engine. The AGN-heated dust distributions turn out to be very compact with sizes on scales of about a parsec in the mid-infrared. Only infrared interferometry currently provides the necessary angular resolution to directly study the physical properties of this dust. Size estimates for the dust distributions derived from interferometric observations can be used to construct a size--luminosity relation for the dust distributions. The large scatter about this relation suggests significant differences between the dust tori in the individual galaxies, even for nuclei of the same class of objects and with similar luminosities. This questions the simple picture of the same dusty doughnut in all AGN. The Circinus galaxy is the closest Seyfert 2 galaxy. Because its mid-infrared emission is well resolved interferometrically, it is a prime target for detailed studies of its nuclear dust distribution. An extensive new interferometric data set was obtained for this galaxy. It shows that the dust emission comes from a very dense, disk-like structure which is surrounded by a geometrically thick, similarly warm dust distribution as well as significant amounts of warm dust within the ionisation cone.