Temperature and Density Distribution in the Molecular Gas Toward
  Westerlund 2: Further Evidence for Physical Association
  Furukawa et al. 2009 reported the existence of a large mass of molecular gas
associated with the super star cluster Westerlund 2 and the surrounding HII
region RCW49, based on a strong morphological correspondence between NANTEN2
12CO(J=2-1) emission and Spitzer IRAC images of the HII region. We here present
temperature and density distributions in the associated molecular gas at 3.5 pc
resolution, as derived from an LVG analysis of the 12CO(J=2-1), 12CO(J=1-0) and
13CO(J=2-1) transitions. The kinetic temperature is as high as 60-150 K within
a projected distance of 5-10 pc from Westerlund 2 and decreases to as low as 10
K away from the cluster. The high temperature provides robust verification that
the molecular gas is indeed physically associated with the HII region,
supporting Furukawa et al.'s conclusion. The derived temperature is also
roughly consistent with theoretical calculations of photo dissociation regions
(PDRs), while the low spatial resolution of the present study does not warrant
a more detailed comparison with PDR models. We suggest that the molecular
clouds presented here will serve as an ideal laboratory to test theories on
PDRs in future higher resolution studies.
