Speaker: Marko Stalevski (Astronomical Observatory of Belgrade, Serbia)
Title: Towards a new paradigm of dust in active galactic nuclei: dissecting the Circinus galaxy
Abstract: To understand the growth of supermassive black holes (SMBHs) and hence their relationship with host galaxies, we need to understand what active galactic nuclei (AGN) are like and how they work. AGN are powered by matter spiraling into a SMBH in the form of an accretion disk. A dusty structure, often dubbed “the dusty torus”, is assumed to surround the black hole and the accretion disk, absorb the radiation coming from the disk and re-emit it in the infrared. However, recent high angular resolution observations resolved for the first time the mid-infrared (MIR) structure of nearby AGN. Surprisingly, they revealed that a major fraction of their MIR emission comes from the polar region, at odds with the classic picture in which dust is to be found around the equatorial plane. When facing a potential change of paradigm, case studies of objects with the best intrinsic resolution are essential. One such source with a clear detection of polar dust is a nearby, well-known AGN in the Circinus galaxy. Recent MIR interferometry and single dish imaging have cast this galaxy in a major role as a prototype of the newly recognized population of ‘polar dust AGN’. In this picture, a major fraction of the MIR emission is associated with dusty winds blown away from the sublimation zone by radiation pressure. I will present our recent and ongoing efforts to understand the obscuring and outflowing structures in Circinus using MIR imaging, optical polarimetry, IFS and X-ray data, tied together by state-of-the-art radiative transfer simulations. All the evidence paints a consistent picture of a compact dusty disk responsible for the obscuration and feeding of the black hole, and a dusty outflow in the polar direction, which extends into the ionization cone and produces some peculiar features in interaction with the immediate surroundings in the host galaxy.