Probing photoionization models in two well-studied extended emission-line regions - Centaurus A and 3C 227

Viegas, Sueli M.; Prieto, M. A.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 258, no. 3, p. 483-490.

Advertised on:
10
1992
Number of authors
2
IAC number of authors
0
Citations
34
Refereed citations
30
Description
The observed emission-line ratios of the extended emission-line regions of Cen A and 3C 227 are compared with the theoretical results from photoionization models, assuming a power-law spectrum for the nuclear ionizing radiation. We show that a variation of the optical depth of the emitting gas can mimic a variation of the ionization parameter. Most of the observational data are explained if each subregion in the extended emission-line gas is characterized by a different value of the optical depth and shows a small density contrast between a 'cloud' and a more dilute gas. However, the observed forbidden O III line ratio cannot be reproduced by photoionization, and an additional heating mechanisms is required. Solar abundances give the best fit to the observations. However, for most subregions the (N/O) ratio is between solar and half solar.