Non-ideal MHD simulations of subcritical prestellar cores with non-equilibrium chemistry

Abstract

Non-ideal magnetohydrodynamic (MHD) effects are thought to be gravity's closest ally in overcoming the support of magnetic fields and in forming stars. Here, we modify the publicly available version of the adaptive mesh refinement code FLASH (Fryxell et al. 2000; Dubey et al. 2008) to include a detailed treatment of non-ideal MHD and study such effects in collapsing prestellar cores. We implement two very extended non-equilibrium chemical networks, the largest of which is comprised of $\sim$ 300 species and includes a detailed description of deuterium chemistry. The ambipolar-diffusion, Ohmic and Hall resistivities are then self-consistently calculated from the abundances of charged species. We present a series of 2-dimensional axisymmetric simulations where we vary the chemical model, cosmic-ray ionization rate, and grain distribution. We benchmark our implementation against ideal MHD simulations and previously-published results. We show that, at high densities ($n_{\rm{H_2}}>~10^6~\rm{cm^{-3}}$), the ion that carries most of the perpendicular and parallel conductivities is not $\rm{H_3^+}$ as was previously thought, but is instead $\rm{D_3^+}$.