Line and continuum emission from the outer regions of accretion discs in active galactic nuclei. II - Radial structure of the disc.

Details Line and continuum emission from the outer regions of accretion discs in active galactic nuclei. II - Radial structure of the disc. Line and continuum emission from the outer regions of accretion discs in active galactic nuclei. II - Radial structure of the disc.

Mar 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...229..292c&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 229, no. 2, March 1990, p. 292-328.

Astronomy and Astrophysics

Astrophysics

77

Accretion Disks, Active Galactic Nuclei, Continuous Radiation, Emission Spectra, Line Spectra, Electron Scattering, Hydrogen Atoms, Hydrogen Ions, Negative Ions

Scientific paper

The radial structure of the outer regions of s stationary alpha disk in the presence of an external X-ray continuum is determined for radii larger than 100 R(G) where the gas pressure dominates. It is shown that the standard approximation of the Kramers opacity or the pure free-free opacity do not apply at any radius. The opacity is either dominated by electron scattering or by absorption due to neutral hydrogen atoms, to H(-) ions, to molecules and to dust. Two illumination models of the disk, schematizing two extreme possible situations, are described. In one model, there ar two symmetrical compact sources of nonthermal radiation located at a given height above the disk; in the other, the radiation of a central source is scattered back toward the disk by a hot diffusing medium. It is shown that the ionization parameter in the bulk of the irradiated layers is generally small. The line emission of the accretion disk is computed, and the line flux emitted at each radius of the disk is obtained. It is found that, in Seyfert galaxies and low-luminosity quasars, the broad low-ionization lines can be almost entirely due to the disk emission. The fit of the line profiles and line intensities can be used to deduce the physical parameters of the disk and of the illumination model.

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