Abstract

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 ?2798 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 central black hole mass, Fe ii(UV)/Mg ii 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. © 2009 RAS.