Testing the global star formation relation: An HCO+ (3-2) mapping study
  of Red MSX sources in the Bolocam Galactic Plane Survey
  We present an analysis of the relation between the star formation rate (SFR)
and mass of dense gas in Galactic clumps and nearby galaxies. Using the
bolometric luminosity as a measure of SFR and the molecular line luminosity of
HCO+ (3-2) as a measure of dense gas mass, we find that the relation between
SFR and M_{dense} is approximately linear. This is similar to published results
derived using HCN (1-0) as a dense gas tracer. HCO+ (3-2) and HCN (1-0) have
similar conditions for excitation. Our work includes 16 Galactic clumps that
are in both the Bolocam Galactic Plane Survey and the Red MSX Survey, 27 water
maser sources from the literature, and the aforementioned HCN (1-0) data. Our
results agree qualitatively with predictions of recent theoretical models which
state that the nature of the relation should depend on how the critical density
of the tracer compares with the mean density of the gas.
