Photoionization models for liners : gas distribution abundances.
Abstract
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).
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 1985
- Bibcode:
- 1985A&A...143..334B
- Keywords:
-
- 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;
- Astrophysics