Quiescent and Coherent Cores from Gravoturbulent Fragmentation

We investigate the velocity structure of protostellar cores that result from non-magnetic numerical models of the gravoturbulent fragmentation of molecular cloud material. A large fraction of the cores analyzed are “quiescent”; i.e., have non-thermal linewiths smaller or equal to the thermal linewidth. Specifically, about 23 % of the cores have subsonic turbulent line-of-sight velocity dispersions σturb ≤ cs. A total of 46 % are“transonic”, with cs < σturb ≤ 2cs. More than half of our sample cores are identified as “coherent”, i.e., with σturb roughly independent of column density. Of these, about 40 % are quiescent, 40 % are transonic, and 20 % are supersonic. The fact that dynamically evolving cores in highly supersonic turbulent flows can be quiescent may be understood because cores lie at the stagnation points of convergent turbulent flows, where compression is at a maximum, and relative velocity differences are at a minimum. The apparent coherence may be due, at least in part, to an observational effect related to the length and concentration