Other
Scientific paper
Apr 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apj...353..123k&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 353, April 10, 1990, p. 123-131.
Other
19
Absorption Spectra, Abundance, Interstellar Gas, Quasars, Lyman Alpha Radiation, Photoionization, Resonance Scattering, Spectral Line Width
Scientific paper
It is shown here that a large enhancement (greater than 2) of the abundances of heavy elements over solar values may not be necessary to explain the observed strengths of the broad absorption lines of quasars. Even through the C IV 1549-A, N V 1240-A, Si IV 1397-A, and Mg II 2798-A opacities are smaller than the Ly-alpha opacity, their absorptions, as compared with that of Ly-alpha, can be much stronger than what are expected based on the opacity ratios. This possibility arises if the absorption occurs in a clumpy flow in which the Ly-alpha opacity through a cloudlet is large but the cloudlets do not completely cover the background source, while the doublet nature of the C IV, N V, Si IV, and Mg II transitions provides a greater coverage in velocity space for those transitions. It is also found that there is a stronger filling-in of the Ly-alpha absorption. Due to recombination and cascade following Lyman-continuum photoionization, collisional excitation, and other processes, the filling-in of the Ly-alpha absorption is about twice as much as what is expected from resonance scattering alone.
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