Астрофизический семинар САО РАН
28 сентября 2015, 13:30, малый зал
Konrad Tristram (ESO)
Disks and cones: resolving the dusty torus of Active Galactic Nuclei with mid-infrared interferometry
Active galactic nuclei (AGN) are the manifestations of accretion onto the supermassive black hole in the centre of a galaxy. AGN are the most powerful, long-lived objects in the Universe and thought to play a major role for galaxy evolution. A toroidal distribution of molecular gas and dust is a key component in our current picture of active galactic nuclei. This so-called "molecular torus“ is held responsible for the orientation dependent obscuration of the central engine, and it plays a fundamental role for the accretion onto the supermassive black hole. The thermal emission of dust is one of the main possibilities to study this dusty torus. Observations using interferometry in the mid-infrared have, in the last ten years, resolved and characterised this emission beyond simple fits of spectral energy distributions, leading to a great leap forward in our view of the dusty material surrounding AGN.
I will present the most recent results of such observations, obtained with the instrument MIDI. More than 25 active nuclei could be observed with MIDI, showing that the dust distributions are parsec sized. The sizes roughly scale with the square root of the luminosity, albeit with a much large scatter than in the near-infrared. Detailed studies of a few well resolved sources, among them the illustrious nuclei of NGC1068 and the Circinus galaxy, show a two component structure: an inner disk-like emission region which is surrounded by a polar elongated emitter. The latter shows differential absorption in line with the one-sided ionisation cones observed in the optical. These results are in qualitative agreement with recent hydrodynamic simulations of AGN tori. In general, they confirm the concept of a dusty obscurer providing viewing-angle dependent obscuration of the central engine.