The correlation of dust and gas emission in star-forming environments
Monthly Notices of the Royal Astronomical Society
Oxford University Press (OUP) on behalf of the Royal Astronomical Society
We present ammonia maps of portions of the W3 and Perseus molecular clouds in order to compare gas emission with submillimetre continuum thermal emission which are commonly used to trace the same mass component in star-forming regions, often under the assumption of local thermodynamic equilibrium (LTE). The Perseus and W3 star-forming regions are found to have significantly different physical characteristics consistent with the difference in size scales traced by our observations. Accounting for the distance of theW3 region does not fully reconcile these differences, suggesting that there may be an underlying difference in the structure of the two regions. Peak positions of submillimetre and ammonia emission do not correlate strongly. Also, the extent of diffuse emission is only moderately matched between ammonia and thermal emission. Source sizes measured from our observations are consistent between regions, although there is a noticeable difference between the submillimetre source sizes with sources in Perseus being significantly smaller than those in W3. Fractional abundances of ammonia are determined for our sources which indicate a dip in the measured ammonia abundance at the positions of peak submillimetre column density. Virial ratios are determined which show that our sources are generally bound in both regions, although there is considerable scatter in both samples. We conclude that sources in Perseus are bound on smaller scales than in W3 in a way that may reflect their previous identification as low-and high-mass, respectively. Our results indicate that assumptions of local thermal equilibrium and/or the coupling of the dust and gas phases in star-forming regions may not be as robust as commonly assumed. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
The authors would like to thank Neal Evans and Erik Rosolowsky for insightful and thorough comments on this work which have considerably improved its quality. The authors acknowledge the data analysis facilities provided by the Starlink Project under continual development by the JAC. In addition, the following Starlink packages have been used: Kappa, Cupid, GAIA, Convert and Coco. We would like to thank the helpful staff of the GBT in the collection of data used in this paper related to the project GBT10C_024. LKM is supported by a STFC postdoctoral grant (ST/G001847/1) and DJE is supported by a STFC PhD studentship. This research would not have been possible without the SIMBAD astronomical data base service operated at CDS, Strasbourg, France and the NASA Astrophysics Data System Bibliographic Services.
This is the final version of the article. Available from the publisher via the DOI in this record.
Vol. 440, pp. 1730 - 1752