Magnetohydrodynamic Turbulent Mixing Layers: Equilibrium Cooling Models

We present models of turbulent mixing at the boundaries between hot ( T ~ 10 6 -10 7 K) and warm material ( T ~ 10 4 K) in the interstellar medium, using a three-dimensional magnetohydrodynamic code, with radiative cooling. The source of turbulence in our simulations is a Kelvin-Helmholtz instability, produced by shear between the two media. We find that because the growth rate of the large-scale modes in the instability is rather slow, it takes a significant amount of time (~1 Myr) for turbulence to produce effective mixing. We also find that the total column densities of the highly ionized species (C IV, N V, and O VI) per interface (assuming ionization equilibrium) are similar to previous steady state nonequilibrium ionization models but grow slowly from log N ~ 10 11 to a few × 10 12 cm -2 as the interface evolves. However, the column density ratios can differ significantly from previous estimates, with an order of magnitude variation in N (C )/ N (O ) as the mixing develops.