Distances to Dark Clouds: Comparing Extinction Distances to Maser
  Parallax Distances
  We test two different methods of using near-infrared extinction to estimate
distances to dark clouds in the first quadrant of the Galaxy using large near
infrared (2MASS and UKIDSS) surveys. VLBI parallax measurements of masers
around massive young stars provide the most direct and bias-free measurement of
the distance to these dark clouds. We compare the extinction distance estimates
to these maser parallax distances. We also compare these distances to kinematic
distances, including recent re-calibrations of the Galactic rotation curve. The
extinction distance methods agree with the maser parallax distances (within the
errors) between 66% and 100% of the time (depending on method and input survey)
and between 85% and 100% of the time outside of the crowded Galactic center.
Although the sample size is small, extinction distance methods reproduce maser
parallax distances better than kinematic distances; furthermore, extinction
distance methods do not suffer from the kinematic distance ambiguity. This
validation gives us confidence that these extinction methods may be extended to
additional dark clouds where maser parallaxes are not available.
