Multiphase Gas Nature in the Sub-parsec Region of the Active Galactic Nuclei. I. Dynamical Structures of Dusty and Dust-free Outflow

Abstract

We investigated dusty and dust-free gas dynamics for a radiation-driven sub-parsec-scale outflow in an active galactic nucleus (AGN) associated with a supermassive black hole 10 ^7 M _⊙ and bolometric luminosity 10 ^44 erg s ^−1 based on the two-dimensional radiation-hydrodynamic simulations. A radiation-driven “lotus-like” multi-shell outflow is launched from the inner part ( r ≲ 0.04 pc) of the geometrically thin disk, and it repeatedly and steadily produces shocks as mass accretion continues through the disk to the center. The shape of the dust sublimation radius is not spherical and depends on the angle ( θ ) from the disk plane, reflecting the nonspherical radiation field and nonuniform dust-free gas. Moreover, we found that the sublimation radius of θ ∼ 20°–60° varies on a timescale of several years. The “inflow-induced outflow” contributes to the obscuration of the nucleus in the sub-parsec region. The column density of the dust-free gas is N _H ≳ 10 ^22 cm ^−2 for r ≲ 0.04 pc. Gases near the disk plane ( θ ≲ 30°) can be the origin of the Compton-thick component, which was suggested by the recent X-ray observations of AGNs. The dusty outflow from the sub-parsec region can be also a source of material for the radiation-driven fountain for a larger scale.

Keywords

• Active galactic nuclei
• Hydrodynamical simulations
• Astrophysical dust processes
• Hydrodynamics