Other
Scientific paper
Jun 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979mnras.187..871n&link_type=abstract
Monthly Notices of the Royal Astronomical Society, vol. 187, June 1979, p. 871-882.
Other
92
Astronomical Spectroscopy, Emission Spectra, Quasars, Cosmic Dust, Helium, Interstellar Extinction, Line Spectra, Oxygen Spectra, Photoionization
Scientific paper
The emission-line spectra of quasars show various indications of having undergone significant wavelength-dependent extinction. Several observed line ratios are discussed, and it is shown that the He II 1640-A/He II 4686-A and O I 1303-A/O I 8446-A intensity ratios are probably the best reddening indicators. The recent observations of 3C 273 and NGC 4151 show that in both the intrinsic L-alpha/H-beta intensity ratio is about 10 times larger than observed; similar conclusions are reached for a composite sample of quasars. The differential extinction is probably caused by dust near the quasars and affects lines and continuum. By correcting for reddening it is possible to construct a type of photoionization model which is in some ways more satisfactory than previous models. Quasars and Seyfert galaxies may be almost an order of magnitude more luminous than is currently thought, and there are other remarkable implications.
Davidson Kris
Netzer Hagai
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