Mining for Dust in Type 1 Quasars
  We explore the extinction/reddening of ~35,000 uniformly selected quasars
with 0<z<5.3 in order to better understand their intrinsic optical/ultraviolet
spectral energy distributions. Using rest-frame optical-UV photometry taken
from the Sloan Digital Sky Survey's (SDSS) 7th data release, cross-matched to
WISE in the mid-infrared, 2MASS and UKIDSS in the near-infrared, and GALEX in
the UV, we isolate outliers in the color distribution and find them well
described by an SMC-like reddening law. A hierarchical Bayesian model with a
Markov Chain Monte Carlo sampling method was used to find distributions of
powerlaw indices and E(B-V) consistent with both the broad absorption line
(BAL) and non-BAL samples. We find that, of the ugriz color-selected type 1
quasars in SDSS, 2.5% (13%) of the non-BAL (BAL) sample are consistent with
E(B-V)>0.1 and 0.1% (1.3%) with E(B-V)>0.2. Simulations show both populations
of quasars are intrinsically bluer than the mean composite, with a mean
spectral index (${\alpha}_{\lambda}$) of -1.79 (-1.83). The emission and
absorption-line properties of both samples reveal that quasars with
intrinsically red continua have narrower Balmer lines and stronger ionizing
spectral lines, the latter indicating a harder continuum in the extreme-UV and
the former pointing to differences in black hole mass and/or orientation.
