CIV Emission Line Properties and Systematic Trends in Quasar Black Hole
  Mass Estimates
  Black-hole masses are crucial to understanding the physics of the connection
between quasars and their host galaxies and measuring cosmic black hole-growth.
At high redshift, z > 2.1, black hole masses are normally derived using the
velocity-width of the CIV broad emission line, based on the assumption that the
observed velocity-widths arise from virial-induced motions. In many quasars,
the CIV-emission line exhibits significant blue asymmetries (`blueshifts') with
the line centroid displaced by up to thousands of km/s to the blue. These
blueshifts almost certainly signal the presence of strong outflows, most likely
originating in a disc wind. We have obtained near-infrared spectra, including
the H$\alpha$ emission line, for 19 luminous ($L_{Bol}$ = 46.5-47.5 erg/s)
Sloan Digital Sky Survey quasars, at redshifts 2 < z < 2.7, with CIV emission
lines spanning the full-range of blueshifts present in the population. A strong
correlation between CIV-velocity width and blueshift is found and, at large
blueshifts, > 2000 km/s, the velocity-widths appear to be dominated by
non-virial motions. Black-hole masses, based on the full width at half maximum
of the CIV-emission line, can be overestimated by a factor of five at large
blueshifts. A larger sample of quasar spectra with both CIV and H$\beta$, or
H$\alpha$, emission lines will allow quantitative corrections to CIV-based
black-hole masses as a function of blueshift to be derived. We find that
quasars with large CIV blueshifts possess high Eddington luminosity ratios and
that the fraction of high-blueshift quasars in a flux-limited sample is
enhanced by a factor of approximately four relative to a sample limited by
black hole mass.
