The environment of weak emission-line quasars
  The nature of weak emission-line quasars (WLQs) is probed by comparing the
Baldwin effect (BEff) in WLQs and normal quasars (QSOs). We selected 81
high-redshift (z>2.2) and 2 intermediate-redshift (z=1.66 and 1.89) WLQs. Their
rest-frame equivalent widths (EWs) of the C IV emission-line and their
Eddington ratio were obtained from the Sloan Digital Sky Survey Data Release 7
(SDSS DR7) Quasar Catalogue or from Diamond-Stanic et al. We compare the
parameters of WLQs with these of 81 normal quasars from Bright Quasar Survey
(BQS) and 155 radio-quiet and radio-intermediate quasars detected by SDSS and
Chandra. The influence of the Eddington ratio, Lbol/Ledd, and the X-ray to
optical luminosity ratio,alpha_ox, on the BEff is analysed. We find that WLQs
follow a different relationship on the EW(CIV)-Lbol/Ledd plane than normal
quasars. This relationship disagrees with the super-Eddington hypothesis. The
weakness/absence of emission-lines in WLQs does not seem to be caused by their
extremely soft ionizing continuum but by low covering factor (Omega) of their
broad line region (BLR). Comparing emission-line intensities indicates that the
ratios of high-ionization line and low-ionization line regions (i.e.
Omega_(HIL)/Omega_(LIL)) are lower in WLQs than in normal QSOs. The covering
factor of the regions producing C IV and Lyalpha emission-lines are similar in
both WLQs and QSOs.
