Quasar Elemental Abundances at High Redshifts

We examine rest-frame ultraviolet spectra of 70 high redshift quasars (z>3.5)to study the chemical enrichment history of the gas closely related to thequasars, and thereby estimate the epoch of first star formation. The fluxes ofseveral ultraviolet emission lines were investigated within the framework ofthe most recent photoionization models to estimate the metallicity of the gasassociated with the high-z quasars. Standard photoionization parameters and theassumption of secondary nitrogen enrichment indicate an average abundance ofZ/Z_sol = 4 to 5 in the line emitting gas. Assuming a time scale of t_evol =0.5 - 0.8 Gyrs for the chemical enrichment of the gas, the first major starformation for quasars with z>=4 should have started at a redshift of z_f = 6 -8, corresponding to an age of the universe of several 10^8 yrs (H_o = 65km/s/Mpc, Omega_M = 0.3, Omega_Lambda = 0.7). We note that this also appears tobe the era of re-ionization of the universe. Finally, there is some evidencefor a positive luminosity - metallicity relation in this high redshift quasarsample.Comment: 18 pages, 8 figures. accepted for publication in Astrophys.Journal, V589, June