The Bolocam Galactic Plane Survey. VII. Characterizing the Properties of
  Massive Star-Forming Regions
  We present the results of a GBT survey of NH3(1,1), (2,2), (3,3) lines
towards 631 Bolocam Galactic Plane Survey (BGPS) sources at a range of Galactic
longitudes in the inner Galaxy. We have detected the NH3(1,1) line towards 72%
of our targets (456), demonstrating that the high column density features
identified in the BGPS and other continuum surveys accurately predict the
presence of dense gas. We have determined kinematic distances and resolved the
distance ambiguity for all BGPS sources detected in NH3. The BGPS sources trace
the locations of the Scutum and Sagittarius spiral arms, with the number of
sources peaking between Galactocentric radii of 4-5 kpc. We measure the
physical properties of each source and find that depending on the distance,
BGPS sources are primarily clumps, with some cores and clouds. We have examined
the physical properties as a function of Galactocentric distance, and find a
mean gas kinetic temperature of 15.6 K, and that the NH3 column density and
abundance decrease by nearly an order of magnitude between Galactocentric radii
of 3 - 11 kpc. Comparing sources at similar distances demonstrates that the
physical properties are indistinguishable, which suggests a similarity in clump
structure across the Galactic disk. We have also compared the BGPS sources to
criteria for efficient star formation presented independently by Heiderman et
al. and Lada et al., and massive star formation presented by Kauffmann et al.
48% of our sample should be forming stars (including massive stars) with high
efficiency, and 87% contain subregions that should be efficiently forming
stars. Indeed, we find that 67% of the sample exhibit signs of star formation
activity based on an association with a mid-IR source.
