The Bolocam Galactic Plane Survey -- III. Characterizing Physical
  Properties of Massive Star-Forming Regions in the Gemini OB1 Molecular Cloud
  We present the 1.1 millimeter Bolocam Galactic Plane Survey (BGPS)
observations of the Gemini OB1 molecular cloud complex, and targeted ammonia
observations of the BGPS sources. When paired with molecular spectroscopy of a
dense gas tracer, millimeter observations yield physical properties such as
masses, radii, mean densities, kinetic temperatures and line widths. We detect
34 distinct BGPS sources above 5-sigma=0.37 Jy/beam with corresponding 5-sigma
detections in the ammonia (1,1) transition. Eight of the objects show water
maser emission (20%). We find a mean millimeter source FWHM of 1.12 pc, and a
mean kinetic temperature of 20 K for the sample of 34 BGPS sources. The
observed ammonia line widths are dominated by non-thermal motions, typically
found to be a few times the thermal sound speed expected for the derived
kinetic temperature. We calculate the mass for each source from the millimeter
flux assuming the sources are isothermal and find a mean isothermal mass within
a 120" aperture of 230 +/- 180 solar masses. We find a total mass of 8,400
solar masses for all BGPS sources in the Gemini OB1 molecular cloud,
representing 6.5% of the cloud mass. By comparing the millimeter isothermal
mass to the virial mass within a radius equal to the mm source size calculated
from the ammonia line widths, we find a mean virial parameter (M_vir/M_iso) of
1.0 +/- 0.9 for the sample. We find mean values for the distributions of column
densities of 10^22 cm^-2 for H_2, and 3.0x10^14 cm^-2 for ammonia, giving a
mean ammonia abundance of 3.0x10^-8 relative to H_2. We find volume-averaged
densities on the order of 10^3-10^4 cm^-3. The sizes and densities suggest that
in the Gem OB1 region the BGPS is detecting the clumps from which stellar
clusters form, rather than smaller, higher density cores where single stars or
small multiple systems form.
