Other
Scientific paper
May 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apj...355...88g&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 355, May 20, 1990, p. 88-93.
Other
35
Astronomical Models, Balmer Series, Paschen Series, Seyfert Galaxies, Active Galactic Nuclei, Infrared Spectroscopy, Interstellar Extinction, Optical Thickness
Scientific paper
The class of AGN known as Seyfert 1.8 and Seyfert 1.9 galaxies exhibit weak broad-Balmer emission lines and large Balmer decrements. One theory proposed to explain these characteristics is that the broad-line regions (BLRs) are reddened by dust along the line-of-sight. An alternative theory points out that BLR clouds with low optical depths and low ionization parameters can reproduce the observed line ratios. These two theories predict very different fluxes of the IR hydrogen lines. In order to test the theories this paper presents measurements of the Pa-beta emission lines of 10 intermediate Seyferts. Three objects known to have exhibited extreme spectral variability, NGC 2622, NGC 7603, and Mrk 1018, now all in Seyfert 1 states, are consistent with the reddening theory, as is IRAS 1958-183. Two other objects, Mrk 609 (a Seyfert 1.5) and UGC 7064, are more consistent with the optical-depth/ionization-parameter theory. Hence the Seyfert 1.8/1.9 class is evidently a heterogeneous one.
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