Testing Observational Tracers of Turbulence with Numerical Simulations: Measuring the Sonic Mach Number in Molecular Clouds

摘要

Astrophysical simulations provide a unique opportunity to test and verify observational diagnostics of the physics of the interstellar medium. In these proceedings, we highlight how simulations of MHD turbulence can increase the accuracy and understanding of observational tracers of important plasma parameters, such as the sonic Mach number, in molecular clouds. For this purpose we analyze MHD-simulations which include post-processing to take radiative transfer effects of ~(13)CO emission and absorption into account. We find very good agreement between the linewidth estimated sonic Mach number and the actual sonic Mach number of the simulations for optically thin 13CO. However, we find that opacity broadening causes Ms to be overestimated by a factor of ≈ 1.16 - 1.3 when calculated from optically thick 13CO lines. We also find that there is a dependency on the magnetic field: super-Alfvénic turbulence shows increased line broadening as compared with sub-Alfvénic turbulence for all values of optical depth for the line of sight perpendicular to the mean magnetic field. These results have implications for the observationally derived sonic Mach numberdensity standard deviation (σ_(ρ/<ρ>)) relationship, σ_(ρ/<ρ>)~2 = b~2M_s~2 and the related column density standard deviation (σ_(N/)) sonic Mach number relationship, which we briefly discuss. The turbulence sonic Mach number is an important parameter of star formation models and the results highlighted in these proceedings provide researchers with increased understanding of these parameters derived from observations.