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Observational and theoretical work on abundances in AGN has intensified in recent years. The broad emission-line regions of high redshift QSOs appear to have N/C ratios larger than solar by roughly an order-of-magnitude, and high Fe abundances as well. The abundances may be somewhat lower at smaller redshifts and for less luminous objects. Chemical evolution models can account for the high abundances, and the relative excess of N and Fe, by invoking a combination of rapid star formation and an IMF rich in massive stars. The finite time to produce Fe from Type Ia supernovae offers the potential to contrain cosmological models. An alternative suggestions involves the growth by accretion of stars trapped in an accretion disk.
There is also evidence for high abundances in the gas producing the broad absorption lines of BAL QSOs. Narrow line regions of AGN are affected by grain formation, but the high ionization regions have at least solar iron abundances. Nitrogen is enhanced in some cases.
The high abundances in AGN are at least qualitatively consistent with studies of stellar abundances in galactic nuclei and gradial gradients in interstellar abundances across the disks of spiral galaxies.
