A Mid-Infrared Census of Star Formation Activity in Bolocam Galactic
  Plane Survey Sources
  We present the results of a search for mid-infrared signs of star formation
activity in the 1.1 mm sources in the Bolocam Galactic Plane Survey (BGPS). We
have correlated the BGPS catalog with available mid-IR Galactic plane catalogs
based on the Spitzer Space Telescope GLIMPSE legacy survey and the Midcourse
Space Experiment (MSX) Galactic plane survey. We find that 44% (3,712 of 8,358)
of the BGPS sources contain at least one mid-IR source, including 2,457 of
5,067 (49%) within the area where all surveys overlap (10 deg < l < 65 deg).
Accounting for chance alignments between the BGPS and mid-IR sources, we
conservatively estimate that 20% of the BPGS sources within the area where all
surveys overlap show signs of active star formation. We separate the BGPS
sources into four groups based on their probability of star formation activity.
Extended Green Objects (EGOs) and Red MSX Sources (RMS) make up the highest
probability group, while the lowest probability group is comprised of
"starless" BGPS sources which were not matched to any mid-IR sources. The mean
1.1 mm flux of each group increases with increasing probability of active star
formation. We also find that the "starless" BGPS sources are the most compact,
while the sources with the highest probability of star formation activity are
on average more extended with large skirts of emission. A subsample of 280 BGPS
sources with known distances demonstrates that mass and mean H_2 column density
also increase with probability of star formation activity.
