Dust formation in AGN winds

Abstract

Infrared observations of active galactic nucleus (AGN) reveal emission from the putative dusty circumnuclear 'torus' invoked by AGN unification, that is heated up by radiation from the central accreting black hole (BH). The strong 9.7 and 18 micron silicate features observed in the AGN spectra both in emission and absorption, further indicate the presence of such dusty environments. We present detailed calculations of the chemistry of silicate dust formation in AGN accretion disk winds. The winds considered herein are magnetohydrodynamic (MHD) winds driven off the entire accretion disk domain that extends from the BH vicinity to the radius of BH influence, of order of 1 to 100 pc depending on the mass of the resident BH. Our results indicate that these winds provide conditions conducive to the formation of significant amounts of dust, especially for objects accreting close to their Eddington limit, making AGN a significant source of dust in the universe, especially for luminous quasars. Our models justify the importance of a r to the power -1 density law in the winds for efficient formation and survival of dust grains. The dust production rate scales linearly with the mass of the central BH and varies as a power law of index between 2 to 2.5 with the dimensionless mass accretion rate. The resultant distribution of the dense dusty gas resembles a toroidal shape, with high column density and optical depths along the equatorial viewing angles, in agreement with the AGN unification picture.

22 pages, 17 figures (some have subfigures), Accepted for publication in The Astrophysical Journal

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• The dust-gas AGN torus as constrained from X-ray and mid-infrared observations
• Exploring the link between C IV outflow kinematics and sublimation-temperature dust in quasars
• Exploring the relation between dust mass and galaxy properties using Dusty SAGE
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• The infrared echo of SN2010jl and its implications for shock breakout characteristics
• Molecular gas and dust properties in $z>7$ quasar hosts
• Modelling the evolution and influence of dust in cosmological simulations that include the cold phase of the interstellar medium
• AGN anisotropic radiative feedback set by black hole spin
• Resonant instabilities mediated by drag and electrostatic interactions in laboratory and astrophysical dusty plasmas
• GATOS XI : Excess dust heating in the Narrow Line Regions of nearby AGN revealed with JWST/MIRI
• Silicate emission in a type-2 quasar: JWST/MIRI constraints on torus geometry and radiative feedback
• Type Iax supernovae as a source of iron-rich silicate dust