Testing the global star formation relation: An HCO+ (3-2) mapping study of Red MSX sources in the Bolocam Galactic Plane Survey

TL;DR

This study investigates the relationship between star formation rate and dense gas mass in Galactic and extragalactic sources using HCO+ (3-2) as a tracer, finding a roughly linear correlation consistent with previous studies and theoretical models.

Contribution

It provides the first detailed analysis of the SFR-dense gas relation using HCO+ (3-2) in Galactic clumps, confirming its similarity to HCN (1-0) and theoretical predictions.

Findings

The SFR and dense gas mass relation is approximately linear.

HCO+ (3-2) and HCN (1-0) tracers yield similar excitation conditions.

Results support models linking tracer critical density to gas density.

Abstract

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.