A study of clumping in the Cepheus OB 3 molecular cloud

Abstract

A portion of the Cep OB 3 molecular cloud has been mapped in the (C-13)O (1-0) line on a completely sampled grid with a 1.5-arcmin spacing. A total of 45 individual clouds, or clumps, have been identified in the map, with masses from 3 to 300 solar mass, sizes 3 pc or smaller, and mean densities of a few hundred/cu cm. Power-law correlations are found among the clump properties, namely, M proportional to R exp 2.5 and Delta(v) exp 0.24. These exponents differ somewhat from those found for similar correlations for molecular clouds in previous studies. Determination of the virial masses for the clumps shows that the clumps are not gravitationally bound and must be expanding on a time scale of about 1 Myr. Measurements of the (C-13)O (2-1) line give volume densities of 2000-5000. Comparisons of these densities with the mean volume densities from the (C-13)O (1-0) data suggest that the gas is clumped on a small scale with a volume filling factor of 0.04-0.10.