Ultraviolet Fe II emission in z ∼ 2 quasars

We present spectra of six luminous quasars at z ∼ 2, covering rest wavelengths 1600−3200 Å. The fluxes of the UV Fe II emission lines and Mg II λ2798 doublet, the line widths of Mg II, 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 Fe II(UV)/Mg II flux ratio as a function of the cental black hole mass, Fe II(UV)/Mg II in our z ∼ 2 quasars is systematically greater than in the low-redshift quasars. We confermed 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.