Other
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...440..141g&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 440, no. 1, p. 141-150
Other
45
Active Galactic Nuclei, Balmer Series, Cosmic Dust, Interstellar Extinction, Interstellar Matter, Polarization (Waves), Seyfert Galaxies, Astronomical Polarimetry, Astronomical Spectroscopy, Emission Spectra, H Alpha Line, Ionization, Molecular Clouds
Scientific paper
I present the most complete spectral survey of known Seyfert 1.8 and 1.9 galaxies to date and compare the spectra with previous spectra to search for changes in the broad Balmer emission lines. Nine of the 24 galaxies showed significant spectral variability. Confirming previous work on a smaller sample, I find that NGC 7603 = Mrk 533, Mrk 993, and Mrk 1018 show variability consistent with changes in reddening to the broad-line region (BLR) NGC 7603 in particular has brightened substantially in the past few years. Data on Mrk 915 are sparser, but this object, too, may be showing signs of changing extinction. NGC 2622 = Mrk 1218, another Seyfert which showed variability consistent with reddening changes, has declined in brightness over the past few years, and done so in a manner inconsistent with a simple change in reddening. Spectropolarimetry shows that this object is complicated, however, with multiple paths for photons from the nucleus to reach our line of sight, ruling out any simple model. Two other Seyferts, Mrk 883 and UGC 7064, show variability in broad-line fluxes inconsistent with reddening changes, and their variability is probably due to real changes in the ionizing flux in the BLR. Both objects show no apparent change in their optical, nonthermal continuum fluxes. Analysis of some weak correlations found in the properties of the Seyfert 1.8 and 1.9 galaxies shows that those objects thought to have large Balmer decrements due to low optical depth and low ionization parameters in their BLR clouds have systematically lower H-alphab/H-alphan ratios and higher (O III) luminosities than those objects known to be affected by reddening. The senses of both of these weak correlations are opposite to what is predicted by the low-optical depth, low-ionization parameter explanation for these objects.
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