Line and continuum emission from the outer regions of accretion discs in active galactic nuclei. III. Influence of the illumination model

Details Line and continuum emission from the outer regions of accretion discs in active galactic nuclei. III. Influence of the illumination model Line and continuum emission from the outer regions of accretion discs in active galactic nuclei. III. Influence of the illumination model

Mar 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...229..302d&link_type=abstract

Astronomy and Astrophysics, Vol. 229, p. 302 (1990)

Astronomy and Astrophysics

Astrophysics

47

Scientific paper

In this paper we study the influence of the external illumination on the structure of the accretion disc in an Active Galactic Nucleus. We consider two situations: the point source model, where a compact source of non-thermal radiation located at a given height illuminates the disc; the diffusion model, where the radiation of a central source is scattered back towards the disc by a hot diffusing medium The structure of the inner regions of the disc (R < 10^4^ R_G_) is not modified by the presence of an external radiation flux, but a radiatively heated chromosphere is created above the surface. In the outer regions (R > 10^4^ R_G_) the whole disc is radiatively heated. The main result of this study is to show that the ionization parameter in the bulk of the irradiated layers is small. It may be high only in a small external "skin", but in this case the gas undergoes a thermal instability and is heated to a high temperature. As a consequence the disc will mainly emit a Low Ionization spectrum We determine the optical thickness of the Paschen and Balmer continuum and show that the outer regions of the disc are generally transparent in the visible and opaque in the UV, while the inner regions are opaque in both ranges.

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