Kinematic Distances: A Monte Carlo Method
  Distances to high mass star forming regions (HMSFRs) in the Milky Way are a
crucial constraint on the structure of the Galaxy. Only kinematic distances are
available for a majority of the HMSFRs in the Milky Way. Here we compare the
kinematic and parallax distances of 75 Galactic HMSFRs to assess the accuracy
of kinematic distances. We derive the kinematic distances using three different
methods: the traditional method using the Brand & Blitz (1993) rotation curve
(Method A), the traditional method using the Reid et al. (2014) rotation curve
and updated Solar motion parameters (Method B), and a Monte Carlo technique
(Method C). Methods B and C produce kinematic distances closest to the parallax
distances, with median differences of 13% (0.43 kpc) and 17% (0.42 kpc),
respectively. Except in the vicinity of the tangent point, the kinematic
distance uncertainties derived by Method C are smaller than those of Methods A
and B. In a large region of the Galaxy, the Method C kinematic distances
constrain both the distances and the Galactocentric positions of HMSFRs more
accurately than parallax distances. Beyond the tangent point along longitude=30
degrees, for example, the Method C kinematic distance uncertainties reach a
minimum of 10% of the parallax distance uncertainty at a distance of 14 kpc. We
develop a prescription for deriving and applying the Method C kinematic
distances and distance uncertainties. The code to generate the Method C
kinematic distances is publicly available and may be utilized through an
on-line tool.
