Ultraviolet Fe II Emission in Fainter Quasars: Luminosity Dependences,
  and the Influence of Environments
  We investigate the strength of ultraviolet Fe II emission in fainter quasars
compared with brighter quasars for 1.0 <= z <= 1.8, using the SDSS (Sloan
Digital Sky Survey) DR7QSO catalogue and spectra of Schneider et al., and the
SFQS (SDSS Faint Quasar Survey) catalogue and spectra of Jiang et al. We
quantify the strength of the UV Fe II emission using the W2400 equivalent width
of Weymann et al., which is defined between two rest-frame continuum windows at
2240-2255 and 2665-2695 Ang. The main results are the following. (1) We find
that for W2400 >~ 25 Ang. there is a universal (i.e. for quasars in general)
strengthening of W2400 with decreasing intrinsic luminosity, L3000. (2) In
conjunction with previous work by Clowes et al., we find that there is a
further, differential, strengthening of W2400 with decreasing L3000 for those
quasars that are members of Large Quasar Groups (LQGs). (3) We find that
increasingly strong W2400 tends to be associated with decreasing FWHM of the
neighbouring Mg II {\lambda}2798 broad emission line. (4) We suggest that the
dependence of W2400 on L3000 arises from Ly{\alpha} fluorescence. (5) We find
that stronger W2400 tends to be associated with smaller virial estimates from
Shen et al. of the mass of the central black hole, by a factor ~ 2 between the
ultrastrong emitters and the weak. Stronger W2400 emission would correspond to
smaller black holes that are still growing. The differential effect for LQG
members might then arise from preferentially younger quasars in the LQG
environments.
