AGN Obscuring Tori Supported by Infrared Radiation Pressure

Abstract

Explicit 2D axisymmetric solutions are found to the hydrostaticequilibrium, energy balance, and photon diffusion equations withinobscuring tori around active galactic nuclei (AGNs). These solutionsdemonstrate that infrared radiation pressure can support geometricallythick structures in AGN environments subject to certain constraints: thebolometric luminosity must be roughly ~0.03-1 times the Eddingtonluminosity; and the Compton optical depth of matter in the equatorialplane should be ~1, with a tolerance of about an order of magnitude upor down. Both of these constraints are at least roughly consistent withobservations. In addition, angular momentum must be redistributed sothat the fractional rotational support against gravity rises from theinner edge of the torus to the outer in a manner specific to thedetailed shape of the gravitational potential. This model also predictsthat the column densities observed in obscured AGNs should range from~1022 to ~1024 cm-2.