The vertical structure and radiation fields of accretion discs in the centres of AGNs

Abstract

We describe the construction and main properties of stationary accretion discs that are supposed to produce the high luminosities of Active Galactic Nuclei. It is found that for most parameter combinations the discs are geometrically thin everywhere. However, for high accretion rates and/or low local energy generation rates they may get thick close to the central object. The distributions of the temperature, the gas pressure and the vertical optical depth are characterized by steep gradients close to the surface and very flat stratifications in the inner parts. The ratio of the radiation pressure to the gas pressure varies over several orders of magnitude within a disc. The emergent fluxes can be well approximated by power laws in a wide wavelength range but turn over in the middle or extreme UV range. It is argued that this range is best suited for spectral diagnosis from the continuum.