The Bolocam Galactic Plane Survey. VIII. A Mid-Infrared Kinematic
  Distance Discrimination Method
  We present a new distance estimation method for dust-continuum-identified
molecular cloud clumps. Recent (sub-)millimeter Galactic plane surveys have
cataloged tens of thousands of these objects, but detailed study of their
physical properties requires robust distance determinations. We derive Bayesian
distance probability density functions (DPDFs) for 770 objects from the Bolocam
Galactic Plane Survey in the longitude range 7.5 < l < 65. The DPDF formalism
is based on kinematic distances, and uses external data sets to place prior
distance probabilities to resolve the kinematic distance ambiguity (KDA) for
objects in the inner Galaxy. We present priors related to the mid-infrared
absorption of dust in dense molecular regions and the Galactic distribution of
molecular gas. By assuming a numerical model of Galactic mid-infrared emission
and simple radiative transfer, we match the morphology of millimeter thermal
dust emission with mid-infrared absorption to compute a prior DPDF for distance
discrimination. Selecting objects first from (sub-)millimeter source catalogs
avoids a bias towards the darkest infrared dark clouds (IRDCs) and extends the
range of heliocentric distance and contrast range probed by mid-infrared
extinction. We derive well-constrained KDA resolutions for 618 molecular cloud
clumps, with approximately 15% placed at or beyond the tangent distance.
Objects sufficiently dark to be cataloged as IRDCs are generally placed at the
near kinematic distance. Distance comparisons with Galactic Ring Survey KDA
resolutions yield a 92% agreement, and a Galactic face-on view reveals sections
of the Sagittarius and Scutum-Centaurus Arms. This KDA-resolution method for
large catalogs of sources through the combination of (sub-)millimeter and
mid-infrared observations of molecular cloud clumps is generally applicable to
other dust-continuum Galactic plane surveys.
