1212.1429 (L. K. Morgan et al.)

The Correlation of Dust and Gas Emission in Star-Forming Environments    [PDF]

L. K. Morgan, T. J. T. Moore, D. J. Eden, J. Hatchell, J. S. Urquhart

We present ammonia maps of portions of the W3 and Perseus molecular clouds in order to compare gas emission with continuum thermal emission. These are commonly expected to trace the same mass component in star-forming regions, often under the assumption of LTE. The star-forming regions are found to have different physical characteristics consistent with their identification as low-mass and high-mass respectively. Accounting for the distance of the W3 region does not fully reconcile these differences, suggesting that there is 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 submillimeter source sizes in the two observed regions. Fractional abundance measurements of ammonia indicate a dip in abundance at the positions of peak submillimetre flux. Although, we find that depletion of ammonia in our sources is unlikely. Virial ratios are determined which show that sources in Perseus are generally not gravitationally bound and that sources in W3 are, although there is considerable scatter in both samples. We find that this that external pressure is necessary for cores at small scales to be bound while sources and clusters are gravitationally bound on larger scales. 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. Alternatively, the assumption that ammonia and thermal emission trace the same mass component in these regions may need to be revisited, along with the degree to which the excitation conditions within a star-forming region vary.

View original: http://arxiv.org/abs/1212.1429