The Comparison of Physical Properties Derived from Gas and Dust in a Massive Star-Forming Region

TL;DR

This study compares gas and dust properties in a massive star-forming region, revealing temperature discrepancies and implications for observational probes of star formation stages.

Contribution

It provides a detailed comparison of gas and dust temperatures and densities in a massive IRDC, highlighting potential decoupling in young regions and informing observational strategies.

Findings

Dust temperatures are lower than gas temperatures in the coldest regions.

Gas and dust are not well-coupled in the youngest star-forming areas.

Millimeter observations can probe various core types, not just hot cores.

Abstract

We explore the relationship between gas and dust in massive star-forming regions by comparing 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 NH3 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 NH3 abundance, 4.6 x 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 ~ 11.6 +/- 0.2 K vs. T_gas ~ 15.2 +/- 1.5 K), which may indicate that the gas and dust are not well-coupled in the youngest regions (~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 NH3 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.