SIMBAD references

We present spectra of six luminous quasars at z ∼ 2, covering rest wavelengths 1600-3200 Å. The fluxes of the UV Feii emission lines and Mgii λ2798 doublet, the line widths of Mgii and the 3000 Å luminosity were obtained from the spectra. These quantities were compared with those of low-redshift quasars at z = 0.06-0.55 studied by Tsuzuki et al. In a plot of the Feii(UV)/Mgii flux ratio as a function of the central black hole mass, Feii(UV)/Mgii in our z ∼ 2 quasars is systematically greater than in the low-redshift quasars. We confirmed that luminosity is not responsible for this excess. It is unclear whether this excess is caused by rich Fe abundance at z ∼ 2 over low-redshift or by non-abundance effects such as high gas density, strong radiation field and high microturbulent velocity.