Statistical Properties of Line Centroid Velocity Increments in the rho Ophiuchi Cloud
Résumé
We present a comparison of histograms of CO (2-1) line centroid velocity increments in the rho Ophiuchi molecular cloud with those computed for spectra synthesized from a three-dimensional, compressible, but non-star-forming and nongravitating, hydrodynamic simulation. Histograms of centroid velocity increments in the rho Oph cloud clearly show non-Gaussian wings similar to those found in histograms of velocity increments and derivatives in experimental studies of laboratory and atmospheric flows, as well as numerical simulations of turbulence. The magnitude of these wings increases monotonically with decreasing separation, down to the angular resolution of the data. This behavior is consistent with that found in the phase of the simulation that has most of the properties of incompressible turbulence. The time evolution of the magnitude of the non-Gaussian wings in the histograms of centroid velocity increments in the simulation is consistent with the evolution of the vorticity in the flow. We cannot exclude, however, the possibility that the wings are associated with the shock interaction regions. Moreover, the effects of shocks may be more important in an active star-forming region like the rho Oph cloud than in the simulation; however, being able to identify shock interaction regions in the interstellar medium is also important, since numerical simulations show that vorticity is generated in shock interactions.
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