Determination of density structure in dark clouds from CS observations

The emission of the J = 1-0 and J = 2-1 transitions of CS in the three dark clouds TMC-1, L134 N, and B335 was observed. The J = 2-1 profiles for B335 and L134 N indicate that self-absorption by foreground lower excitation material is probably occurring. There is no obvious evidence for self-absorption in the J = 1-0 profiles in these two clouds or in any of the CS lines in TMC-1. The density structure of the clouds is determined by using CS emission as a probe. A large-velocity-gradient radiative transfer model is used to compute the excitation of CS as a function of CS abundance and density and thereby to determine the column density and space density in the clouds. B335 is centrally condensed and TMC-1 and L134 N are fragmented into two or more condensations. The observed structure may be indicative of an early phase of star formation.