We explore the relationship between gas and dust in massive star-forming regions by comparing the physical properties derived from each .
We compare the temperatures and column densities in a massive star-forming Infrared Dark Cloud ( IRDC , G32.02 + 0.05 ) , which shows a range of evolutionary states , from quiescent to active .
The gas properties were derived using radiative transfer modeling of the ( 1,1 ) , ( 2,2 ) , and ( 4,4 ) transitions of NH _ { 3 } on the Karl G. Jansky Very Large Array ( VLA ) , while the dust temperatures and column densities were calculated using cirrus-subtracted , modified blackbody fits to Herschel data .
We compare the derived column densities to calculate an NH _ { 3 } abundance , \chi _ { NH _ { 3 } } = 4.6 \times 10 ^ { -8 } .
In the coldest star-forming region , we find that the measured dust temperatures are lower than the measured gas temperatures ( mean and standard deviations T _ { dust,avg } \sim 11.6 \pm 0.2 K vs. T _ { gas,avg } \sim 15.2 \pm 1.5 K ) , which may indicate that the gas and dust are not well-coupled in the youngest regions ( \sim 0.5 Myr ) or that these observations probe a regime where the dust and/or gas temperature measurements are unreliable .
Finally , we calculate millimeter fluxes based on the temperatures and column densities derived from NH _ { 3 } which suggest that millimeter dust continuum observations of massive star-forming regions , such as the Bolocam Galactic Plane Survey or ATLASGAL , can probe hot cores , cold cores , and the dense gas lanes from which they form , and are generally not dominated by the hottest core .