[IPARCOS astro-seminar] 29/09/2021
Dr. Almudena Prieto (Instituto de Astrofísica de Canarias, Spain)
Dust in the central parsecs of AGN: challenges to the torus and the feeding of Black Holes
Abstract: A parsec-scale dusty torus is thought to be the cause of Active Galactic Nuclei (AGN) dichotomy in the 1/ 2 types, narrow / broad emission lines. During the last few years, within the PARSEC project, we have been producing parsec-scale resolution optical / infrared dust maps of the central kpc of the nearest AGN. The analysis of these dust maps is the focus of this presentation. I will show that dust filaments and lanes are ubiquitous features to the centre of galaxies regardless of their activity level. These filaments are hundred to kpc long, few parsecs wide, very reminiscent of those seen in the ISM of the Milky Way. Depending on their position with respect to the nucleus, their optical thickness and the brightness of the galactic nucleus, a fully or partially obscured nucleus may arise. Their large scale length is found to naturally account for the often conical gas structures seen in ionised gas in AGN. The optical thickness of these filaments changes along their structure, in type 2 reaching optical depths high enough to obscure the nucleus in full. Their location with respect to the nucleus and their increasing optical depth towards the centre could naturally lead to the canonical type 1 / 2 AGN classification. It is thus concluded that these structures may fulfil the role of the putative parsecs-scale torus. The filaments and lanes are traced by equivalent structures in molecular cold and warm gas in CO, HCN and H2. A single filament can be seen either getting straight- or spiralling- to the centre, suggesting their role as streamers channelling material from galactic scales to the centre to feed the AGN. Inflow rates of a few tenth to one solar mass per year, depending on Eddington luminosity, are inferred.
