The Correlation of Dust and Gas Emission in Star-Forming Environments
  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 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 the W3 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.
