From Thin to Thick: the Impact of X-ray Irradiation on Accretion Disks in Agn

We argue that the X-ray and UV flux illuminating the parsec-scale accretion disk around luminous active galactic nuclei (AGN) is super-Eddington with respect to the local far-infrared dust opacity. The far infrared opacity may be larger than in the interstellar medium of the Milky Way due to a combination of supersolar metallicity and the growth of dust grains in the dense accretion disk. Because of the irradiating flux, the outer accretion disk puffs up with a vertical thickness h ∼ R. This provides a mechanism for generating a geometrically thick obscuring region from an intrinsically thin disk. We find obscuring columns ∼ 10 − 10 cm, in reasonable agreement with observations. Subject headings: galaxies: active – galaxies: Seyfert – galaxies: nuclei – accretion, accretion disks – dust, extinction