Detection of Iron Emission in the z = 5.74 QSO SDSSp J104433.04-012502.2
  We obtained near-infrared spectroscopy of the z=5.74 QSO, SDSSp J104433.04-012 502.2 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 A) 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 Balmer continuum. The rest equivalent width of Fe II (3000-3500 A) is ~30 A which is similar to those of low redshift QSOs measured by the same manner. The chemical enrichment models that assume the life time of the progenitor of SNe Ia is longer than 1 Gyr predict that weaker Fe II emission than low red shift. However, none of the observed high redshift (z > 3) QSOs show a systematic dec rease of Fe II emission compared with low redshift QSOs. This may due to a shorter lifetime of SNe Ia in QSO nuclei than in the solar neighborhood. Another reason of strong Fe II emission at z=5.74 may be longer cosmological age due to smaller Omega_M. 
K. Aoki, T. Murayama, K. Denda