Dust in the central parsecs of unobscured AGN: more challenges to the torus

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. In a previous work, on the basis of parsec-scale resolution infrared / optical dust maps it was found that dust filaments, few parsecs wide, several hundred parsecs long, were ubiquitous features crossing the centre of type 2 AGN, their optical thickness being sufficient to fully obscure the optical nucleus. This work presents the complementary view for type 1 and intermediate-type AGN. The same type of narrow, collimated, dust filaments are equally found at the centre of these AGN. The difference now resides in their location with respect to the nucleus, next to it but not crossing it, as it is the case in type 2, and their reduced optical thickness towards the centre, $A_V\lesssim 1.5\mathrm{mag}$, insufficient to obscure at UV nucleus wavelengths. It is concluded that large scale, hundred pc to kpc long, dust filaments and lanes, reminiscent of those seen in the Milky Way, are a common ingredient to the central parsec of galaxies. Their optical thickness 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 increasing gradient in optical depth towards the centre could naturally lead to the canonical type 1/2 AGN classification, making these filaments to play the role of the torus. Dust filaments and lanes show equivalent morphologies in molecular gas. Available gas kinematic indicates mass inflows at rates $<1M\odot y{r}^{-1}$.

20 pages, 14 figures, accepted in MNRAS (07-Jun-2021)

References in corpus (14)

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Cited by in corpus (6)

• Thermal imaging of dust hiding the black hole in the Active Galaxy NGC 1068
• The Past and Future of Mid-Infrared Studies of AGN
• The Black Hole-Galaxy Connection: Interplay between Feedback, Obscuration, and Host Galaxy Substructure
• VLTI/GRAVITY Interferometric Measurements of Innermost Dust Structure Sizes around AGNs
• The Accretion Mode in Sub-Eddington Supermassive Black Holes: Getting into the Central Parsecs of Andromeda
• ReveaLLAGN 1: JWST Emission-Line Spectra Reveal Low-Luminosity AGN with UV-Deficient SEDs and Warm Molecular Gas