Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985a%26a...143..334b&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 143, no. 2, Feb. 1985, p. 334-346.
Astronomy and Astrophysics
Astrophysics
61
Emission Spectra, Galactic Nuclei, Gas Dynamics, Interstellar Gas, Line Spectra, Photoionization, Abundance, Astronomical Models, Galactic Structure, H Ii Regions, Interstellar Chemistry, Ionized Gases, Optical Thickness, Spectral Correlation
Scientific paper
Low-ionization nuclear emission regions (Liners) in galaxies are characterized on the basis of a statistical analysis of all available observational data and a review of theoretical models based on photoionization by the nonthermal UV spectrum. The results are presented in graphs and tables and characterized in detail. A good correlation which is unaffected by reddening or geometrical parameters and includes objects with Balmer lines or X-ray flux is found by plotting the ratio of forbidden O III to (H-alpha)/3 against the forbidden (O I)/(O III) ratio. Models based on photoionization by a nonstellar object and having power-law index -2.0 and near-solar metallicity are computed; the O/N abundance ratio is found to vary by a factor of three or less; the nuclear-gas abundances of O, N, and S are seen as approximately uniform; the characteristics of the brightest objects are attributed to optically thin clouds or to nuclear H II regions; and Liners are shown to form a subgroup of normal galaxies with emission lines, with no physically based separation from other higher-excitation objects (except Seyfert galaxies).
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