Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1975
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975sva....18..720i&link_type=abstract
(Astronomicheskii Zhurnal, vol. 51, Nov.-Dec. 1974, p. 1208-1224.) Soviet Astronomy, vol. 18, May-June 1975, p. 720-729. Transl
Astronomy and Astrophysics
Astronomy
3
Astronomical Models, Astronomical Spectroscopy, Emission Spectra, Galactic Nuclei, Seyfert Galaxies, Electron Density (Concentration), Forbidden Bands, Gas Ionization, Line Spectra, Luminous Intensity, Nebulae, Power Spectra, Radial Distribution
Scientific paper
Models are considered for the gas shells of the nuclei of six Seyfert galaxies. The gas, which is responsible for the emission-line spectra of these galaxies, is shown to be in a quasi-equilibrium state and is ionized by a central source with a power-law spectrum. Equations of ionization equilibrium and energy balance are solved together by the method of successive approximations, and the degree of ionization is determined for H, He, O, Ne, N, and S. A two-component model is adopted in which a dense region is surrounded by a slowly expanding corona or halo. The theoretical and observed spectra are compared, and the mass of the radiating gas is determined along with the external diameter of the region where the emission-line spectrum originates. It is suggested that forbidden O II, N II, and S II ions emit in a layer of gas 11 to 14 pc thick situated in the outer parts of the shell. The best agreement between theoretical and observed dimensions occurs when the spacing factor falls between 0.0001 and 0.001. Using the nuclei of NGC 4151 and 7469 as an example, the necessity of inserting the dense region in the models of some nuclei is demonstrated.
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