Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei

Abstract

We present self-consistent models of the vertical structure and emergent spectrum of active galactic nucleus (AGN) accretion disks. The central object is assumed to be a supermassive Kerr black hole. We demonstrate that non-LTE (NLTE) effects and the effects of a self-consistent vertical structure of a disk play a very important role in determining the emergent radiation and therefore should be taken into account. In particular, NLTE models exhibit a largely diminished H I Lyman discontinuity when compared to LTE models, and the He II discontinuity appears strongly in emission for NLTE models. Consequently, the number of ionizing photons in the He II Lyman continuum predicted by NLTE disk models is 1–2 orders of magnitude higher than that following from the blackbody approximation. This prediction has important implications for ionization models of AGN broad-line regions and for models of the intergalactic radiation field and the ionization of helium in the intergalactic medium.