High‐Mass Star Formation. I. The Mass Distribution of Submillimeter Clumps in NGC 7538

We present submillimeter continuum maps at 450 and 850 microns of a 12 x 8arcminute region of the NGC 7538 high-mass star-forming region, made using theSubmillimeter Common-User Bolometer Array (SCUBA) on the James Clerk MaxwellTelescope. We used an automated clump-finding algorithm to identify 67 clumpsin the 450 micron image and 77 in the 850 micron image. Contrary to previousstudies, we find a positive correlation between high spectral index, alpha, andhigh submillimeter flux, with the difference being accounted for by differenttreatments of the error beam. We interpret the higher spectral index atsubmillimeter peaks as a reflection of elevated dust temperature, particularlywhen there is an embedded infrared source, though it may also reflect changingdust properties. The clump mass-radius relationship is well-fit by a power lawof the form M \propto R^(-x) with x = 1.5-2.1, consistent with theories ofturbulently-supported clumps. According to our most reliable analysis, thehigh-mass end (approx. 100-2700 M_sun) of the submillimeter clump mass functionin NGC 7538 follows a Salpeter-like power law with index 2.0 +/- 0.3. Thisresult agrees well with similar studies of lower-mass regions rho Oph and OrionB. We interpret the apparent invariance of the shape of the clump mass functionover a broad range of parent cloud masses as evidence for the self-similarityof the physical processes which determine it. This result is consistent withmodels which suggest that turbulent fragmentation, acting at early times, issufficient to set the clump mass function.Comment: 37 pages, 7 figures, accepted for publication in Ap