2017ApJ...840...48P

We compute the star-formation rate (SFR) in molecular clouds (MCs) that originate ab initio in a new, higher-resolution simulation of supernova-driven turbulence. Because of the large number of well-resolved clouds with self-consistent boundary and initial conditions, we obtain a large range of cloud physical parameters with realistic statistical distributions, which is an unprecedented sample of star-forming regions to test SFR models and to interpret observational surveys. We confirm the dependence of the SFR per free-fall time, SFR_ff, on the virial parameter, α_vir, found in previous simulations, and compare a revised version of our turbulent fragmentation model with the numerical results. The dependences on Mach number, M , gas to magnetic pressure ratio, β, and compressive to solenoidal power ratio, χ at fixed α_vir are not well constrained, because of random scatter due to time and cloud-to-cloud variations in SFR_ff. We find that SFR_ff in MCs can take any value in the range of 0 <= SFR_ff <= 0.2, and its probability distribution peaks at a value of SFR_ff ≃ 0.025, consistent with observations. The values of SFR_ff and the scatter in the SFR_ff-α_vir relation are consistent with recent measurements in nearby MCs and in clouds near the Galactic center. Although not explicitly modeled by the theory, the scatter is consistent with the physical assumptions of our revised model and may also result in part from a lack of statistical equilibrium of the turbulence, due to the transient nature of MCs.