Ultraviolet Fe II emission in z ~ 2 quasars
  We present spectra of six luminous quasars at z ~ 2, covering rest
wavelengths 1600-3200 A. The fluxes of the UV Fe II emission lines and Mg II
2798 doublet, the line widths of Mg II, and the 3000 A 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.
