The Star Formation Rate of Supersonic Mhd Turbulence

This work revisits the star formation rate (SFR) model of Krumholz and McKee, extends it to the case of a magnetized medium, and verifies it with a set of numerical simulations of driven, supersonic, magneto-hydrodynamic (MHD) turbulence, where collapsing cores are captured with accreting sink particles. The main results are: i) a new physical interpretation of the critical density for star formation not based on the concepts of turbulent pressure support and sonic scale; ii) the derivation of the critical density in the MHD case and the derivation of the corresponding MHD model of the SFR, predicting a lower SFR and a stronger dependence on the virial parameter than the hydrodynamic (HD) model; iii) the demonstration that driven supersonic turbulence results in a constant SFR, after an initial transient phase with increasing SFR; iv) the derivation of the SFR in the simulations as a function of the virial parameter, shown to agree well with the SFR predicted by the MHD model, and less with the prediction of the HD model, potentially due to the important role of the Kelvin-Helmholtz instability of postshock shear layers in the HD case. A physical model of the SFR is needed for implementing the star formation feedback in simulations of galaxy formation. We suggest that the new star formation law derived in this paper be implemented in future galaxy formation simulations. Subject headings: ISM: kinematics and dynamics – MHD – stars: formation – turbulence