Journal Article Sub-parsec-scale dynamics of a dusty gas disc exposed to anisotropic AGN radiation with frequency-dependent radiative transfer

Namekata, Daisuke  ,  Umemura, Masayuki

460 ( 1 )  , pp.980 - 1018 , 2016-07 , Oxford University Press
We explore the gas dynamics near the dust sublimation radius of active galactic nucleus (AGN). For the purpose, we perform axisymmetric radiation hydrodynamic simulations of a dusty gas disc of radius ≈1 pc around a supermassive black hole of mass 107 M⊙ taking into account (1) anisotropic radiation of accretion disc, (2) X-ray heating by corona, (3) radiative transfer of infrared (IR) photons re-emitted by dust, (4) frequency dependence of direct and IR radiations, and (5) separate temperatures for gas and dust. As a result, we find that for Eddington ratio ≈0.77, a nearly neutral, dense (≈106--8cm−3), geometrically thin (h/r < 0.06) disc forms with a high-velocity (≈200 ∼ 3000 km s−1) dusty outflow launched from the disc surface. The disc temperature is determined by the balance between X-ray heating and various cooling, and the disc is almost supported by thermal pressure. Contrary to Krolik (2007), the radiation pressure by IR photons is not effective to thicken the disc, but rather compresses it. Thus, it seems difficult for a radiation-supported, geometrically thick, obscuring torus to form near the dust sublimation radius as far as the Eddington ratio is high (∼1). The mass outflow rate is 0.05--0.1M⊙yr−1 and the column density of the outflow is NH ≲ 1021 cm−2. To explain observed type-II AGN fraction, it is required that outflow gas is extended to larger radii (r ≳ 10 pc) or that a denser dusty wind is launched from smaller radii (r ∼ 104 Rg).

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