Deuterium Chemodynamics of Massive Pre-Stellar Cores

High levels of deuterium fractionation of N₂H⁺ (i.e., D_frac(N₂H⁺) > 0.1) are often observed in pre-stellar cores (PSCs) and detection of N₂D⁺ is a promising method to identify elusive massive PSCs. However, the physical and chemical conditions required to reach such high levels of deuteration are still uncertain, as is the diagnostic utility of N₂H⁺ and N₂D⁺ observations of PSCs. Here we carry out a series of three-dimensional magnetohydrodynamics simulations of a massive, turbulent prestellar core, coupled with a sophisticated deuteration astrochemical network. We investigate the effects of initial ortho-para ratio of H₂ (OPR^H2), temperature, cosmic ray (CR) ionization rate, CO and N-species depletion factors and prior chemical evolution of the PSC. We find that high CR ionization rates and high depletion factors allow the simulated D_frac(N₂H⁺) and absolute abundances to match observational values in about one free-fall time. For OPR^H2, while a lower initial value helps the growth of D_frac(N₂H⁺), the spatial structure of deuteration in this case is too widespread compared to observed systems. For an example model with elevated CR ionization rates and significant heavy element depletion, we then study the kinematic and dynamic properties of the core as traced by its N₂D⁺ emission. The core, undergoing quite rapid collapse, exhibits disturbed kinematics in its average velocity map. Still, because of magnetic support, the core often appears kinematically sub-virial based on its N₂D⁺ velocity dispersion. We discuss the implications of our results for massive star formation theories.