Temperature and Density Distribution in the Molecular Gas Toward Westerlund 2: Further Evidence for Physical Association

Furukawa et al. reported the existence of a large mass of molecular gas associated with the super star cluster Westerlund 2 and the surrounding H II region RCW49, based on a strong morphological correspondence between NANTEN2 (12)CO(J = 2-1) emission and Spitzer IRAC images of the H II region. We here present temperature and density distributions in the associated molecular gas at similar to 3.5 pc resolution, as derived from a large velocity gradient analysis of the (12)CO(J = 2-1), (12)CO(J = 1-0), and (13)CO(J = 2-1) transitions. The kinetic temperature is as high as similar to 60-150 K within a projected distance of similar to 5-10 pc from Westerlund 2 and decreases to as low as similar to 10 K away from the cluster. The high temperature provides robust verification that the molecular gas is indeed physically associated with the H II region, supporting Furukawa et al.'s conclusion. The derived temperature is also roughly consistent with theoretical calculations of photodissociation 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.