Biases in the Quasar Mass-Luminosity Plane
  We find that the recently reported departure from the Eddington luminosity
limit for the highest quasar black hole masses at a given redshift is an
artifact due to biases in black hole mass measurements. This sub-Eddington
boundary (with non-unity slope) in the quasar mass-luminosity plane was
initially reported by Steinhardt & Elvis (2010a) using the FWHM-based black
hole mass catalogue of Shen et al. (2008). However, the significance of the
boundary is reduced when the FWHM-based mass-scaling relationship is
recalibrated following Wang et al. (2009) and using the most updated
reverberation mapping estimates of black hole masses. Furthermore, this
boundary is not seen using mass estimates based on the line dispersion of the
same quasars' MgII emission lines. Thus, the initial report of a sub-Eddington
boundary with non-unity slope was due to biases in estimating masses using the
FWHM of a fit of one or two Gaussians to quasar MgII emission lines. We provide
evidence that using the line dispersion of the MgII line produces less biased
black hole mass estimates.
