High‐Redshift Quasars and Star Formation in the Early Universe

In order to derive information on the star formation history in the earlyuniverse we observed 6 high-redshift (z=3.4) quasars in the near-infrared tomeasure the relative iron and \mgii emission strengths. A detailed comparisonof the resulting spectra with those of low-redshift quasars show essentiallythe same FeII/MgII emission ratios and very similar continuum and line spectralproperties, indicating a lack of evolution of the relative iron to magnesiumabundance of the gas since z=3.4 in bright quasars. On the basis of currentchemical evolution scenarios of galaxies, where magnesium is produced inmassive stars ending in type II SNe, while iron is formed predominantly in SNeof type Ia with a delay of ~1 Gyr and assuming as cosmological parameters H_o =72 km/s Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7$, we conclude that majorstar formation activity in the host galaxies of our z=3.4 quasars must havestarted already at an epoch corresponding to z_f ~= 10, when the age of theuniverse was less than 0.5 Gyrs.Comment: 29 pages, 5 figures, ApJ in pres