Gemini Near-Infrared Spectroscopy of Luminousz~ 6 Quasars: Chemical Abundances, Black Hole Masses, and MgiiAbsorption

We present Gemini near-infrared spectroscopic observations of six luminous quasars at z=5. 86. 3. Five of them were observed using Gemini-South/GNIRS, which provides a simultaneous wavelength coverage of 0. 9--2. 5 μm in cross dispersion mode. The other source was observed in K band with Gemini-North/NIRI. We calculate line strengths for all detected emission lines and use their ratios to estimate gas metallicity in the broad-line regions of the quasars. The metallicity is found to be supersolar with a typical value of 4 Z_, and a comparison with low-redshift observations shows no strong evolution in metallicity up to z6. The FeII/MgII ratio of the quasars is 4. 9+/-1. 4, consistent with low-redshift measurements. We estimate central BH masses of 10⁹ to 10^10 M_ and Eddington luminosity ratios of order unity. We identify two MgII λλ2796, 2803 absorbers with rest equivalent width W₀^2796>1 Åat 2. 21. 5 Åat z>3 in the spectra, with the two most distant absorbers at z=4. 8668 and 4. 8823, respectively. The redshift number densities (dN/dz) of MgII absorbers with W₀^2796>1. 5 Åare consistent with no cosmic evolution up to z>4.