Schedule Aug 14, 2007
Intermittency and Dissipative Structures of ISM Turbulence
Edith Falgarone (ENS-OP)

One important issue regarding the role of interstellar turbulence in the star formation process is its distribution among the different scales and its dissipation. In incompressible turbulence, the transfer rate of the energy and its dissipation are intermittent in space and time. For interstellar turbulence, magnetized and compressible, intermittency is still an elusive concept. In this perspective, observed statistical and structural signatures of intermittency are presented and compared in two parsec-scale samples of gas, chosen in different large scale environments, a high latitude cloud and a more massive cloud, already forming stars.

Large and small scale properties are found to be coupled, the most turbulent field at the parsec scale being the most intermittent at small scale. Intermittent elongated structures are found in both samples, parallel to the direction of the local magnetic field. In the most turbulent field, the thinnest structures (less than 0.01 pc) cluster into a thicker coherent pattern which extends over several pc. A dissipation lengthscale is inferred from the comparison of these data with recent numerical simulations. Such a scale, combined with the special chemical and thermal properties observed in these structures, supports the view that they are dissipative structures of interstellar turbulence. These results raise several challenges that will be addressed.

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