Far-UV Fe Emission as Proxy of Eddington Ratios
  The Eddington ratio is a key parameter that governs the diversity of quasar
properties. It can be scaled with a strong anti-correlation between optical Fe
II and [O III] emission. In search of such indicators in the far-UV band, the
HST far-UV spectra of 150 low-redshift quasars are analyzed in combination with
their optical SDSS counterparts. The strength of Fe II+Fe III 1123 emission is
significantly correlated with that of optical Fe II. A moderate correlation may
also exist between Fe II 1071 and optical Fe II. The finding opens the
possibility that far-UV Fe II emission may serve as a new gauge of the
Eddington ratios. The high- and low-ionization lines in the far-UV band display
different patterns: for the quasars with higher Eddington ratios, the
low-ionization UV lines are stronger, and the high-ionization lines are broader
and weaker.
