The nature of turbulence in OMC1 at the scale of star formation: observations and simulations

¹ Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark e-mail: maikeng@phys.au.dk
² NORDITA, Blegdamsvej 17, 2100 Copenhagen $\emptyset$, Denmark
³ Observatoire de Paris & Université de Cergy-Pontoise, LERMA & UMR 8112 du CNRS, 92195 Meudon, France

Received: 7 December 2005
Accepted: 12 April 2006

Abstract

Aims.To study turbulence in the Orion Molecular Cloud (OMC1) by comparing observed and simulated characteristics of the gas motions.

Methods. Using a dataset of vibrationally excited H₂ emission in OMC1 containing radial velocity and brightness which covers scales from 70 AU to 30 000 AU, we present the structure functions and the scaling of the structure functions with their order. These are compared with the predictions of two-dimensional projections of simulations of supersonic hydrodynamic turbulence.

Results. The structure functions of OMC1 are not well represented by power laws, but show clear deviations below 2000 AU. However, using the technique of extended self-similarity, power laws are recovered at scales down to 160 AU. The scaling of the higher order structure functions with order deviates from the standard scaling for supersonic turbulence. This is explained as a selection effect of preferentially observing the shocked part of the gas and the scaling can be reproduced using line-of-sight integrated velocity data from subsets of supersonic turbulence simulations. These subsets select regions of strong flow convergence and high density associated with shock structure. Deviations of the structure functions in OMC1 from power laws cannot however be reproduced in simulations and remains an outstanding issue.