Elemental abundances in the broad emission line region of quasars at redshifts larger than 4

We present observations of 11 high redshift quasars (3.9 less than or similar to z less than or similar to 5.0) observed with low spectral resolution in the restframe ultraviolet using FORS 1 at the VLT UT 1. The emission-line fluxes of strong permitted and intercombination ultraviolet emission lines are measured to estimate the chemical composition of the line emitting gas. Comparisons to photoionization calculations indicate gas metallicities in the broad emission line region in the range of solar to several times solar. The average of the mean metallicity of each high-z quasar in this sample is Z/Z., = 4.3 +/- 0.3. Assuming a chemical evolution time scale of tau(evol) similar or equal to 0.5 - 0.8 Gyrs, we derive a redshift of z(f) similar or equal to 6 to 8 for the onset of the first major star formation episode (H-0 = 65 km s(-1) Mpc(-1), Omega(M) = 0.3, Omega(A) = 0.7), corresponding to an age of the universe of several 10(8) yrs at this epoch. We note that this epoch is also supposed to be the era of re-ionization of the universe.