Molecular clumps in the W51 giant molecular cloud

Abstract

In this paper, we present a catalogue of dense molecular clumps located within the W51 giant molecular cloud (GMC). This work is based on Heterodyne Array Receiver Programme 13CO J = 3–2 observations of the W51 GMC and uses the automated CLUMPFIND algorithm to decompose the region into a total of 1575 clumps of which 1130 are associated with the W51 GMC. We clearly see the distinct structures of the W51 complex and the high-velocity stream previously reported. We find the clumps have characteristic diameters of 1.4 pc, excitation temperatures of 12 K, densities of 5.6 × 1021 cm−2, surface densities 0.02 g cm−2 and masses of 90 M⊙. We find a total mass of dense clumps within the GMC of 1.5 × 105 M⊙, with only 1 per cent of the clumps detected by number and 4 per cent by mass found to be supercritical. We find a clump-forming efficiency of 14 ± 1 per cent for the W51 GMC and a supercritical clump-forming efficiency of per cent. Looking at the clump mass distribution, we find it is described by a single power law with a slope of above ∼100 M⊙. By comparing locations of supercritical clumps and young clusters, we see that any future star formation is likely to be located away from the currently active W51A region.