Clumpy outer Galaxy molecular clouds and the steepening of the IMF

We report the results of high-resolution (similar to 0.2 pc) CO (1-0) and C S (2-1) observations of the central regions of three star-forming molecular clouds in the far-outer Galaxy (similar to 16 kpc from the Galactic Center ): WB89 85 (Sh 2-127), WB89 380, and WB89 437. We used the BIMA array in co mbination with IRAM 30-m and NRAO 12-m observations. The GMC's in which the regions are embedded were studied by means of KOSMA 3-m CO (2-1) observati ons (here we also observed WB89 399). We compare the BIMA maps with optical , radio, and near-infrared observations. Using a clumpfind routine, structu res found in the CO and CS emission are subdivided in clumps, the propertie s of which are analyzed and compared with newly derived results of previous ly published single-dish measurements of local clouds (OrionB South and Ros ette). We find that the slopes of the clump mass distributions (-1.28 and -1.49, f or WB89 85 and WB89 380, respectively) are somewhat less steep than found f or most local clouds, but similar to those of clouds which have been analyz ed with the same clumpfind program. We investigate the clump stability by using the virial theorem, including a ll possible contributions (gravity, turbulence, magnetic fields, and pressu re due to the interclump gas). It appears that under reasonable assumptions a combination of these forces would render most clumps stable. Comparing o nly gravity and turbulence, we find that in the far-outer Galaxy clouds, th ese forces are in equilibium (virial parameter alpha approximate to 1) for clumps down to the lowest masses found (a few M-.). For clumps in the local clouds alpha approximate to 1 only for clumps with masses larger than a fe w tens of M-.. Thus it appears that in these outer Galaxy clumps gravity is the dominant force down to a much lower mass than in local clouds, implyin g that gravitational collapse and star formation may occur more readily eve n in the smallest clumps. Although there are some caveats, due to the inhom ogeneity of the data used, this might explain the apparently steeper IMF fo und in the outer Galaxy.