Detection of iron emission in the z=5.74 QSO SDSSp J104433.04-012502.2

obtained near-infrared spectroscopy of the z = 5.74 QSO SDSSp J104433.04-012502.2, with the Infrared Camera and Spectrograph of the Subaru Telescope. The redshift of 5.74 corresponds to a cosmological age of 1.0 Gyr for the current Lambda-dominated cosmology. We found a similar strength of the Fe II (3000-3500 Angstrom) emission lines in SDSSp J104433.04-012502.2 as in low-redshift QSOs. This is the highest redshift detection of iron. We subtracted a power-law continuum from the spectrum and fitted model Fe II emission and the Balmer continuum. The rest equivalent width of Fe II (3000-3500 Angstrom) is similar to 30 Angstrom, which is similar to those of low-redshift QSOs measured in the same manner. The chemical-enrichment models that assume the lifetime of the progenitor of SNe la is longer than 1 Gyr predict that weaker Fe II emission in high-redshift (z > 3) QSOs than low-redshift ones. However, none of the observed high redshift QSOs show a systematic decrease of Fell emission compared with low-redshift QSOs. This may be due to a shorter lifetime of SNe Ia in QSO nuclei than in the solar neighborhood. Another reason for the strong Fe II emission at z = 5.74 may be a longer cosmological age due to a smaller Omega(M).