Gemini near-infrared spectroscopy of luminous z ∼ 6 quasars:: Chemical abundances, black hole masses, and MgII absorption

We present Gemini near-infrared spectroscopic observations of six luminous quasars at z = 5.8 to similar to 6.3. Five of them were observed using Gemini South GNIRS, which provides a simultaneous wavelength coverage of 0.9-2.5 mu m in cross-dispersion mode. The other source was observed in the 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 similar to 4Z(circle dot), and a comparison with low-redshift observations shows no strong evolution in metallicity up to z similar to 6. The Fe II/Mg II ratio of the quasars is 4.9 +/- 1.4, consistent with low-redshift measurements. We estimate central black hole masses of 10(9)-10(10)M(circle dot) and Eddington luminosity ratios of order unity. We identify two Mg II lambda lambda 2796, 2803 absorbers with rest equivalent width Wk(0)(lambda 2796) > 1 angstrom at 2.2 < z < 3 and three Mg II absorbers with W-0(lambda 2796) > 1.5 angstrom at 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 Mg II absorbers with W-0(lambda 2796) > 1.5 angstrom are consistent with no cosmic evolution up to z > 4.