Metallicities and Abundance Ratios from Quasar Broad Emission Lines

The broad emission lines (BELs) of quasars and active galactic nuclei (AGNs)are important diagnostics of the relative abundances and overall metallicity inthe gas. Here we present new theoretical predictions for several UV BELs. Wefocus specifically on the relative nitrogen abundance as a metallicityindicator, based on the expected secondary enrichment of nitrogen atmetallicities Z > 0.2 Z_o. Among the lines we consider, N III] 1750/O III]1664, N V 1240/(C IV 1549 + O VI 1034) and N V/He II 1640 are the most robustdiagnostics. We argue, in particular, that the average N V BEL is not dominatedby scattered Ly-alpha photons from a broad absorption line wind. We thencompare our calculated line ratios with observations from the literature. Theresults support earlier claims that the gas-phase metallicities near quasarsare typically near or several times above the solar value. We conclude thatquasar activity is preceded by, or coeval with, an episode of rapid andextensive star formation in the surrounding galactic (or proto-galactic)nuclei. Chemical evolution models of these environments suggest that, to reachZ > Z_o in well-mixed interstellar gas, the star formation must have begun >10^8 yr before the observed quasar activity.Comment: 15 pages, 5 figures in 6 files, in press with ApJ. This version fixes some minor glitches and includes previously omitted reference