Annu. Rev. Astron. Astrophys. 1999. 37: 487-531
Copyright © 1999 by Annual Reviews. All rights reserved

Reprinted with kind permission from Annual Reviews, 4139 El Camino Way, Palo Alto, California, USA

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ELEMENTAL ABUNDANCES IN QUASISTELLAR OBJECTS:
Star Formation and Galactic Nuclear Evolution at High Redshifts

Fred Hamann

Department of Astronomy, University of Florida, 211 Bryant Space Sciences Center, Gainesville, FL 32611-2055; e-mail: hamann@astro.ufl.edu
and
Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, California 92093-0424

Gary Ferland

Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055; e-mail: gary@pa.uky.edu
and
Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON, M5S 3H8 Canada

Abstract. Quasar (QSO) elemental abundances provide unique probes of high-redshift star formation and galaxy evolution. There is growing evidence from both the emission and intrinsic absorption lines that QSO environments have roughly solar or higher metallicities out to redshifts >4. The range is not well known, but solar to a few times solar metallicity appears to be typical. There is also evidence for higher metallicities in more luminous objects and for generally enhanced N/C and Fe / alpha abundances compared with solar ratios.

These results identify QSOs with vigorous, high-redshift star formation - consistent with the early evolution of massive galactic nuclei or dense protogalactic clumps. However, the QSOs offer new constraints. For example, (a) most of the enrichment and star formation must occur before the QSOs "turn on" or become observable, on time scales of ltapprox 1 Gyr at least at the highest redshifts. (b) The tentative result for enhanced Fe/ alpha suggests that the first local star formation began at least ~ 1 Gyr before the QSO epoch. (c) The star formation must ultimately be extensive to reach high metallicities; that is, a substantial fraction of the local gas must be converted into stars and stellar remnants. The exact fraction depends on the shape of the initial mass function (IMF). (d) The highest derived metallicities require IMFs that are weighted slightly more toward massive stars than in the solar neighborhood. (e) High metallicities also require deep gravitational potentials. By analogy with the well-known mass-metallicity relation among low-redshift galaxies, metal-rich QSOs should reside in galaxies (or protogalaxies) that are minimally as massive (or as tightly bound) as our own Milky Way.