Ultraviolet Fe II emission in z ~ 2 quasars

TL;DR

This study analyzes ultraviolet Fe II emission in six luminous quasars at z ~ 2, finding an excess compared to low-redshift quasars that may be due to higher Fe abundance or other physical conditions.

Contribution

First measurement of UV Fe II emission in z ~ 2 quasars and comparison with low-redshift data to explore evolution and physical conditions.

Findings

Fe II(UV)/Mg II flux ratio is higher in z ~ 2 quasars.

Luminosity does not account for the excess Fe II emission.

Uncertain whether excess is due to Fe abundance or physical conditions.

Abstract

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.