Physical conditions in low-luminosity active galactic nuclei
Physical conditions in the nuclei of emission-line galaxies are investigated by analyzing their continua and optical emission lines. The strength and shape of the nonstellar continuum is derived from nine Seyfert galaxies. As in QSOs, it is described by a power law with slope approx. -1.1 and, in the most luminous objects it flattens at blue and uv wavelengths. Even at a minimum brightness it has no short wavelength cutoff near 1 ..mu..m, eliminating the possibility that the near infrared flux is dominated by thermal emission from hot dust grains. A detailed analysis at optical and x-ray energies demonstrates that gas in the nucleus of NGC 7213 is photoionized by nonstellar radiation, even though it also exhibits the spectral characteristics of galaxies thought to be heated by shocks. After careful removal of the strong stellar component, it is shown how these shock features are actually more consistent with photoionization. The key is a large range of densities (approx.10/sup 3/-10/sup 7/ cm/sup -3/) in the narrow-line clouds, and a fairly low ionization parameter. Similar studies of three additional galaxies confirm these results and strengthen the hypothesis that gas in LINERs (low ionization nuclear emission-line regions) is photoionized rather than shock-heated.
- Research Organization:
- California Inst. of Tech., Pasadena (USA)
- OSTI ID:
- 5364607
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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