METALLICITY IN QUASAR AGN ENVIRONMENT - A CONSEQUENCE OF USUAL OR UNUSUAL STAR-FORMATION

Recent observations indicate that the heavy-element abundances in quasars, in particular in gas flowing out of the nuclear regions, may be larger than solar. Abundances do not depend significantly on the age of quasars (redshift from low to approximately 5). The nuclear metallicity may be rapidly generated and maintained at approximately time-stationary values. We review two mechanisms proposed for the metallicity enrichment of quasars and, in general, all active galactic nuclei (AGN). One is the familiar, though unusually rapid (starburst-like) star formation cycle, which is external to the AGN. The other mechanism, occurring inside AGN, is a seeded massive star formation involving a capture of seed stars from the host galaxy's nucleus by an assemblage of clouds or by an accretion disk orbiting the central massive, compact object (e.g., black hole). We outline some of the recent results and prospects for future work within the second scenario. The results indicate that the observed metallicities in high-redshift quasars do not necessarily imply that global star formation and efficient chemical changes have occurred throughout their host galaxies at early cosmological epochs.