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 Source 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.