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Issue A&A Volume 412, Number 2, December III 2003 Page(s) 417 - 430 Section Formation, structure and evolution of stars DOI 10.1051/0004-6361:20031474

A&A 412, 417-430 (2003)
DOI: 10.1051/0004-6361:20031474

Non-Gaussian velocity shears in the environment of low mass dense cores

J. Pety^{1, 2} and E. Falgarone<sup>1

1</sup>  LERMA/LRA, Observatoire de Paris & École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
²  Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France
    e-mail: pety@iram.fr; falgarone@lra.ens.fr

(Received 10 April 2002 / Accepted 4 September 2003 )

Abstract
We report on a novel kind of small scale structure in molecular clouds found in IRAM-30m and CSO maps of  ¹²CO and ¹³CO lines around low mass starless dense cores. These structures come to light as the locus of the extrema of velocity shears in the maps, computed as the increments at small scale (~ 0.02 pc) of the line velocity centroids. These extrema populate the non-Gaussian wings of the shear probability distribution function (shear-PDF) built for each map. They form elongated structures of variable thickness, ranging from less than 0.02 pc for those unresolved, up to 0.08 pc. They are essentially pure velocity structures. We propose that these small scale structures of velocity shear extrema trace the locations of enhanced dissipation in interstellar turbulence. In this picture, we find that a significant fraction of the turbulent energy present in the field would be dissipating in structures filling less than a few % of the cloud volume.

Key words: ISM: evolution -- ISM: kinematics and dynamics -- ISM: molecules -- ISM: structure -- turbulence

Offprint request: J. Pety, pety@iram.fr

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