Outflow and hot dust emission in broad absorption line quasars
  We have investigated a sample of 2099 broad absorption line (BAL) quasars
with z=1.7-2.2 built from the Sloan Digital Sky Survey Data Release Seven and
the Wide-field Infrared Survey. This sample is collected from two BAL quasar
samples in the literature, and refined by our new algorithm. Correlations of
outflow velocity and strength with hot dust indicator (beta_NIR) and other
quasar physical parameters, such as Eddington ratio, luminosity and UV
continuum slope, are explored in order to figure out which parameters drive
outflows. Here beta_NIR is the near-infrared continuum slope, a good indicator
of the amount of hot dust emission relative to accretion disk emission. We
confirm previous findings that outflow properties moderately or weakly depends
on Eddington ratio, UV slope and luminosity. For the first time, we report
moderate and significant correlations of outflow strength and velocity with
beta_NIR in BAL quasars. It is consistent with the behavior of blueshifted
broad emission lines in non-BAL quasars. The statistical analysis and composite
spectra study both reveal that outflow strength and velocity are more strongly
correlated with beta_NIR than Eddington ratio, luminosity and UV slope. In
particular, the composites show that the entire C IV absorption profile shifts
blueward and broadens as beta_NIR increases, while Eddington ratio and UV slope
only affect the high and low velocity part of outflows, respectively. We
discuss several potential processes and suggest that dusty outflow scenario,
i.e. dust is intrinsic to outflows and may contribute to the outflow
acceleration, is most likely. The BAL quasar catalog is available from the
authors upon request.
