TEMPERATURE AND DENSITY DISTRIBUTION IN THE MOLECULAR GAS TOWARD WESTERLUND 2: FURTHER EVIDENCE FOR PHYSICAL ASSOCIATION

Abstract

Furukawa et al. 2009 reported the existence of a large mass of molecular gas\nassociated with the super star cluster Westerlund 2 and the surrounding HII\nregion RCW49, based on a strong morphological correspondence between NANTEN2\n12CO(J=2-1) emission and Spitzer IRAC images of the HII region. We here present\ntemperature and density distributions in the associated molecular gas at 3.5 pc\nresolution, as derived from an LVG analysis of the 12CO(J=2-1), 12CO(J=1-0) and\n13CO(J=2-1) transitions. The kinetic temperature is as high as 60-150 K within\na projected distance of 5-10 pc from Westerlund 2 and decreases to as low as 10\nK away from the cluster. The high temperature provides robust verification that\nthe molecular gas is indeed physically associated with the HII region,\nsupporting Furukawa et al.'s conclusion. The derived temperature is also\nroughly consistent with theoretical calculations of photo dissociation regions\n(PDRs), while the low spatial resolution of the present study does not warrant\na more detailed comparison with PDR models. We suggest that the molecular\nclouds presented here will serve as an ideal laboratory to test theories on\nPDRs in future higher resolution studies.\n