Passive Tracers in ATHENA: Implementation and Applications to Turbulent Star Formation

Abstract

We implement two passive tracer schemes in the magnetohydrodynamic code ATHENA: a Monte Carlo method by which tracers are moved probabilistically according to the mass flux from a grid cell, and a second-order in time passive tracer scheme which integrates the equation of motion based on the velocity interpolated to a particle’s location. Due to its relative computational efficiency, we apply the Monte Carlo method to the numerical simulation of isothermal turbulence in a molecular cloud. We deposit tracers in dense cores above certain threshold densities and follow the subsequent collapse of the GMC. We present results of incompressive decaying turbulence of clouds with vir = 1 and vir = 1:5. Although the majority of the gas from both high and low density regions eventually collapses, we find that at earlier times, t tff , a much larger proportion of the stellar mass comes from tracers initially in high density regions. This suggests that stars may initially accrete material from the highest-density regions and then accrete from successively lower-density regions. Our results may also imply a relationship between pre-stellar core density and collapse time.