Far-Infrared Dust Temperatures and Column Densities of the MALT90 Molecular Clump Sample

Abstract

We present dust column densities and dust temperatures for similar to 3000 young, high-mass molecular clumps from the Millimeter Astronomy Legacy Team 90 GHz survey, derived from adjusting single-temperature dust emission models to the far-infrared intensity maps measured between 160 and 870 mu m from the Herschel/Herschel Infrared Galactic Plane Survey (Hi-Gal) and APEX/APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) surveys. We discuss the methodology employed in analyzing the data, calculating physical parameters, and estimating their uncertainties. The population average dust temperature of the clumps are 16.8 +/- 0.2 K for the clumps that do not exhibit mid-infrared signatures of star formation (quiescent clumps), 18.6 +/- 0.2 K for the clumps that display mid-infrared signatures of ongoing star formation but have not yet developed an H II region (protostellar clumps), and 23.7 +/- 0.2 and 28.1 +/- 0.3 K for clumps associated with H II and photo-dissociation regions, respectively. These four groups exhibit large overlaps in their temperature distributions, with dispersions ranging between 4 and 6 K. The median of the peak column densities of the protostellar clump population is 0.20 +/- 0.02 g cm(-2), which is about 50% higher compared to the median of the peak column densities associated with clumps in the other evolutionary stages. We compare the dust temperatures and column densities measured toward the center of the clumps with the mean values of each clump. We find that in the quiescent clumps, the dust temperature increases toward the outer regions and that these clumps are associated with the shallowest column density profiles. In contrast, molecular clumps in the protostellar or H II region phase have dust temperature gradients more consistent with internal heating and are associated with steeper column density profiles compared with the quiescent clumps.