Bibcode
Viegas, Sueli M.; Prieto, M. A.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 258, no. 3, p. 483-490.
Fecha de publicación:
10
1992
Número de citas
33
Número de citas referidas
29
Descripción
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.