Massive Clumps in the NGC 6334 Star-forming Region

We report observations of dust continuum emission at 1.2 mm toward the star-forming region NGC 6334 made with the SEST SIMBA bolometer array. The observations cover an area of ~2 deg² with approximately uniform noise. We detected 181 clumps spanning almost 3 orders of magnitude in mass (3-6 × 10³ M_☉) and with sizes in the range 0.1-1.0 pc. We find that the clump mass function dN/d log M is well fit with a power law of the mass with exponent -0.6 (or equivalently dN/dM ∝ M^-1.6). The derived exponent is similar to those obtained from molecular line-emission surveys and is significantly different from that of the stellar initial mass function. We investigated changes in the mass spectrum by changing the assumptions on the temperature distribution of the clumps and on the contribution of free-free emission to the 1.2 mm emission and found little change on the exponent. The cumulative mass distribution function is also analyzed, giving consistent results in a mass range excluding the high-mass end, where a power-law fit is no longer valid. The masses and sizes of the clumps observed in NGC 6334 indicate that they are not direct progenitors of stars and that the process of fragmentation determines the distribution of masses later on or occurs at smaller spatial scales. The spatial distribution of the clumps in NGC 6334 reveals clustering which is strikingly similar to that exhibited by young stars in other star-forming regions. A power-law fit to the surface density of companions gives Σ ∝ θ^-0.62.