Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987a%26a...184...33j&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 184, no. 1-2, Oct. 1987, p. 33-42.
Astronomy and Astrophysics
Astrophysics
54
Active Galactic Nuclei, Balmer Series, Ionization, Spectral Line Width, Heavy Elements, Low Temperature
Scientific paper
Up to now photoionization models of the broad line region of quasars fail to explain the strength of low ionization lines, in particular, Fe II lines are too weak compared to Hβ. Using a code mainly designed to study partly ionized and optically thick media, the radiation transfer in a non-photoionized homogeneous cloud is calculated in order to outline the physical conditions required to explain the observed Fe II intensities. The influence of the physical parameters is described and limiting values are set by the intensities of the other lines emitted by the medium. The main constraint is the Balmer continuum intensity. The results of the computations are compared to the published line ratios of about 30 well-observed AGN. It is shown that if the "Fe II problem" is not easily solved as regard the strong Fe II UV emitters, low temperature high density clouds provide Fe IIopt/Hβ ratios in very good agreement with observations.
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