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The broad emission lines (BELs) of quasars and active galactic nuclei (AGNs) are important diagnostics of the relative abundances and overall metallicity in the gas. Here we present new theoretical predictions for several UV BELs. We focus specifically on the relative nitrogen abundance as a metallicity indicator, based on the expected secondary enrichment of nitrogen at metallicities 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 robust diagnostics. We argue, in particular, that the average N V BEL is not dominated by scattered Ly-alpha photons from a broad absorption line wind. We then compare our calculated line ratios with observations from the literature. The results support earlier claims that the gas-phase metallicities near quasars are typically near or several times above the solar value. We conclude that quasar activity is preceded by, or coeval with, an episode of rapid and extensive star formation in the surrounding galactic (or proto-galactic) nuclei. Chemical evolution models of these environments suggest that, to reach Z > Z_o in well-mixed interstellar gas, the star formation must have begun > 10^8 yr before the observed quasar activity.
The flux ratios of high-ionization lines are commonly assumed to indicate the metallicity of the broad emission line region in luminous quasars. When accounting for the variation in their kinematic profiles, we show that the NV/CIV, (SiIV+OIV])/CIV a
We describe a Bayesian approach to estimating quasar black hole mass functions (BHMF) when using the broad emission lines to estimate black hole mass. We show how using the broad line mass estimates in combination with statistical techniques develope
The broad emission lines commonly seen in quasar spectra have velocity widths of a few per cent of the speed of light, so special- and general-relativistic effects have a significant influence on the line profile. We have determined the redshift of t
The chemical composition of galaxies has been measured out to z~4. However, nearly all studies beyond z~0.7 are based on strong-line emission from HII regions within star-forming galaxies. Measuring the chemical composition of distant quiescent galax
We measure the metal abundance ratios in the X-ray photoionized gas located near the narrow line region of a sample of Seyfert 2 AGN. The high-resolution X-ray spectra observed with the Chandra high- and low-energy transmission grating spectrometers