Dense cores in dark clouds. III - Subsonic turbulence

Using published data, possible correlations among line widths and cloud size are examined for clouds which span the transition between supersonic and subsonic motions. Plots which show linear correlations between log line width and log cloud size, and between log density and log cloud size are presented and discussed, as well as a plot showing that most clouds are close to virial equilibrium. It is concluded that all of the relations among line width, density, and cloud size found for earlier supersonic regions extend into the subsonic regime. If a turbulent energy cascade is present in dense cores, the dissipation of turbulence is likely to be important for cloud heating and star formation. In active star-forming regions, dense cores tend to be more prevalent, denser, smaller, and to have narrower lines than in regions with less star formation. This tendency is expected if dense cores evolve into low-mass stars by dissipating their turbulence.