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J. Ballesteros-Paredes (Inst. de Astronomia, U. Nacional Autonoma de Mexico \& Harvard-Smithsonian CfA), E. Vazquez-Semadeni (Inst. de Astronomia, U. Nacional Autonoma de Mexico)
It has been found recently that small (\lesssim 0.1 pc) dense cores in molecular clouds show a non-thermal velocity dispersion which is independent of size (Goodman et al 1998). We suggest that, rather than being an indication of velocity coherence, such a flat scaling may be interpreted as the signature of the collision between larger-scal gas streams. This is verified in MHD numerical simulations of the ISM. If the relative velocity difference between the streams is not very large, then the mass-weighted velocity histograms, which are the numerical equivalent of optically thin spectra, show a single spectral component of nearly constant width over a range of scales within the core, as long as the shock site remains unresolved.
In this escenario, a core with a size-independent velocity dispersion is not decoupled from its environment, as has been suggested previously. Instead, it is causally and dynamically connected with the external flow.
The author(s) of this abstract have provided an email address for comments about the abstract: javier@astroscu.unam.mx