ELEMENTAL ABUNDANCES OF THE BROAD ABSORPTION-LINE GAS OF QUASARS

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 though the C IV λ1549, N v λ1240, Si IV λ1397, and Mg H II λ2798 opacities are smaller than the Lyα opacity, their absorptions, as compared with that of Lyα, 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 Lyα 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 Lyα absorption. Due to recombination and cascade following Lyman continuum photoionization, collisional excitation, and other processes, the filling-in of the Lyα absorption is about twice as much as what is expected from resonance scattering alone.