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C. M. Gaskell, S. A. Snedden (U. Nebraska)
Observations and photoionization models of the relative strengths of the strong high-ionization UV lines in quasars can be used to estimate the density of broad line region (BLR) clouds. A long-standing problem is that such estimates produce densities an order-of-magnitude or more lower than the densities needed to explain the small BLR sizes found in emission line variability studies. Over the last few years it has become clear that because of rapid enrichment of gas in the centers of galaxies, abundances in quasars are significantly greater than solar. Our analysis of Hubble Space Telescope FOS spectra of quasars using the photoionization code CLOUDY (Ferland 1998) shows that adoption of higher abundances leads to significantly higher BLR density estimates which potentially remove the density discrepancy between photoionization modelling and variability studies. The derived density is higher primarily because of changes in the ionization structure caused by higher metalicity.
The author(s) of this abstract have provided an email address for comments about the abstract: snedden@unlinfo.unl.edu