Statistical properties of line centroid velocity increments in the rho Ophiuchi cloud

We present a comparison of histograms of CO (2-1) line centroid velocity in crements in the rho Ophiuchi molecular cloud with those computed for spectr a synthesized from a three-dimensional, compressible, but non-star-forming and nongravitating, hydrodynamic simulation. Histograms of centroid velocit y increments in the rho Oph cloud clearly show non-Gaussian wings similar t o those found in histograms of velocity increments and derivatives in exper imental studies of laboratory and atmospheric flows, as well as numerical s imulations of turbulence. The magnitude of these wings increases monotonica lly 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 evo lution of the magnitude of the non-Gaussian wings in the histograms of cent roid 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 regi on like the rho Oph cloud than in the simulation; however, being able to id entify shock interaction regions in the interstellar medium is also importa nt, since numerical simulations show that vorticity is generated in shock i nteractions.