Quasars (or QSOs) at all redshifts have strong emission and (sometimes) absorption lines due to metals in their immediate environments. The gas must have undergone some amount of chemical enrichment, presumably via local star formation. At the highest quasar redshifts, approaching z ~ 5 (Schneider et al. 1991), the enrichment time scales cannot be long; the Universe itself was less than (1 + z)-1 17% of its present age at z = 5, or roughly 1 billion years old (depending on the cosmology, see Fig. 1). Quasar metal abundances can therefore provide valuable constraints on the properties of star formation in the early Universe, possibly for the first stars forming in young galactic nuclei or pre-galactic condensations. These constraints will be important complements to other studies of high-redshift galaxies, involving, for example, the ``Lyman-break'' objects (Steidel et al. 1998, Connolly et al. 1997) or damped-Ly absorbers (Pettini et al. 1997, Lu et al. 1998), that probe more extended structures or rely on very different data and analysis techniques. An important goal of quasar research is therefore to merge the QSO abundance results with these other studies to develop a more complete picture of star formation and galaxy evolution at early cosmological epochs.
Quasar abundance studies also naturally address a variety of problems concerning the QSOs themselves, such as the circumstances of QSO formation and evolution, the location, geometry, dynamics and physical conditions of the emission and absorption line regions, the relationships between the various emission and absorption phenomena (including the soft X-ray ``warm'' absorbers), and the influence of metallicity on the physics and observable properties of QSO environments. The last of these items specifically involves the Baldwin Effect (see Osmer & Shields and Korista et al. in this volume).
Three independent probes of QSO abundances are readily observable at all redshifts: the broad emission lines (BELs), the broad absorption lines (BALs) and the intrinsic narrow absorption lines (NALs). Each diagnostic has its own theoretical and observational uncertainties, so it is important to consider as many of them as possible. Here I review the status of QSO abundance studies based on these diagnostics. I will emphasize my own ongoing work with various collaborators. Please see Hamann & Ferland (1999 - hereafter HF99) for a more thorough review of this topic.
Figure 1. Redshift versus age of the Universe in Big Bang cosmologies. The three solid curves correspond to H0 = 65 km s-1 Mpc-1, = 0 and M = 0, 0.3 and 1. The dotted curve corresponds to = 0.7 and M = 0.3. The ``error'' bars show the range of ages possible for H0 between 50 and 80 km s-1 Mpc-1 (see Carroll & Press 1992).