Unusual CO Line Ratios and Kinematics in the N83/N84 Region of the Small Magellanic Cloud

We present new CO 1-0 and 2-1 observations of the N83/N84 molecular cloudcomplex in the south-east Wing of the Small Magellanic Cloud (SMC). While the2-1/1-0 integrated line brightness ratio (in temperature units) is uniformly0.9 throughout most of the complex, we find two distinct regions with unusuallyhigh ratios 2-1/1-0 > 2. These regions are associated with the N84D nebula andwith the inside of the 50 pc expanding molecular shell N83. This shell isspatially coincident with the NGC 456 stellar association and the HFPK2000-448radio continuum/X-ray source tentatively classified as a supernova remnant. Weexplore possible causes for the high ratios observed and conclude that the COemission probably arises from an ensemble of small (R~0.1 pc), warm (T~40 K)clumps. Analysis of the CO shell parameters suggests that it is wind--drivenand has an age of slightly more than 2 million years. We have also used thisdataset to determine the CO-to-H2 conversion factor in the SMC, an especiallyinteresting measurement because of the low metallicity of this source (~1/9solar). Surprisingly, after comparing the CO luminosities of clouds in N83/N84with their virial masses, we find a CO-to-H2 conversion factor Xco only 1.9times larger than what we obtain when applying the same algorithm to solarmetallicity clouds in the Milky Way and M 33. This result fits into theemerging pattern that CO observations with high linear resolution suggestnearly Galactic values of Xco in a wide range of environments.