Magnetic flux transport via reconnection diffusion in different sonic regimes of interstellar MHD turbulence

ABSTRACT Turbulence and magnetic fields are components of the interstellar medium and are interconnected through plasma processes. In particular, the magnetic flux transport in the presence of magnetohydrodynamic (MHD) turbulence is an essential factor for understanding star formation. The theory of reconnection diffusion (RD), based on statistics of Alfvénic turbulence, predicts a dependence of the diffusion coefficient of the magnetic field on the Alfvénic Mach number $M_\mathrm{ A}$. However, this theory does not consider the effects of compressibility which are important in the regime of supersonic MHD turbulence. In this work, we measure the diffusion coefficient of magnetic fields in sub-Alfvénic MHD turbulence, with different sonic Mach numbers $M_\mathrm{ S}$. We perform numerical simulations of forced turbulence in periodic domains from the incompressible limit to the supersonic regime. We introduce two methods to extract the diffusion coefficient, based on the analysis of tracer particles. Our results confirm the RD assumption regarding the correspondence between the diffusion of magnetic field and that of fluid Lagrangian particles. The measured diffusion rate provided by incompressible turbulence agrees with the suppression predicted by the RD theory in the presence of strong magnetic fields: $D \propto M_\mathrm{ A}^3$. Our simulations also indicate an increase in RD efficiency when the turbulence is compressible. The dependency on $M_\mathrm{ A}$ and $M_\mathrm{ S}$ from the simulations can be described by the relation $D \propto M_\mathrm{ A}^{\alpha }$, where $\alpha (M_\mathrm{ S}) \approx 3 / (1 + M_\mathrm{ S})$. This quantitative characterization of D is critical for modelling star formation in turbulent molecular clouds and evaluating the efficiency of this transport compared to other mechanisms.