Obscuring Material around Seyfert Nuclei with Starbursts

Abstract

The structure of obscuring matter in the environment of active galactic nuclei with associated nuclear starbursts is investigated using three-dimensional hydrodynamical simulations. Simple analytical estimates suggest that the obscuring matter with energy feedback from supernovae has a torus-like structure with a radius of several tens of parsecs and a scale height of ∼10 pc. These estimates are confirmed by the fully nonlinear numerical simulations, in which the multiphase inhomogeneous interstellar matter and its interaction with the supernovae are consistently followed. The globally stable, torus-like structure is highly inhomogeneous and turbulent. To achieve the high column densities (≳1024 cm-2) as suggested by observations of some Seyfert 2 galaxies with nuclear starbursts, the viewing angle should be larger than about 70° from the pole-on for a 108 M⊙ massive black hole. Owing to the inhomogeneous internal structure of the torus, the observed column .density is sensitive to the line of sight, and it fluctuates by a factor on the order of ∼100. The covering fraction for N>1023 cm-2 is about 0.4. The average accretion rate toward R < 1 pc is ∼0.4 M ⊙ yr-1, which is boosted to twice that in the model without the energy feedback.