Dissipation of turbulence by magnetohydrodynamic shock waves

Abstract

We characterise steady, one-dimensional fast and slow magnetohydrodynamic (MHD) shocks using a two-fluid model. Fast MHD shocks are magnetically driven, forcing ions to stream through the neutral gas ahead of the shock front. This magnetic precursor heats the gas sufficiently to create a large, warm transition zone where all fluid variables only weakly change in the shock front. In contrast, slow MHD shocks are driven by gas pressure where neutral species collide with ion species in a thin hot slab that closely resembles an ordinary gas dynamic shock.

We computed observational diagnostics for fast and slow shocks at velocities v_s=2–4 km/s and preshock Hydrogen nuclei densities nH = 10^2-4 cm⁻³. We followed the abundances of molecules relevant for a simple oxygen chemistry and include cooling by CO, H2 and H₂O. Estimates of intensities of ¹²CO rotational lines show that high-J lines, above J = 6 → 5, are more strongly excited in slow MHD shocks.