Simulations of the Wardle instability of C-type shock waves

Abstract

C-type shocks in the partially ionized ISM are modelled by numerical simulations. Under certain conditions the shocks are subject to the Wardle instability, which initially makes the shock front rippled, then in the non-linear stage can produce density variations in both the ion and neutral fluids. A systematic search in the numerically accessible parameter space is done to determine the wave vector kmax and the growth rate S max of the fastest growing modes. The neutral Alfven number, and the angle θ s between the shock normal and the upstream magnetic field determine the strength and obliqueness of the shock, as well as the dimensionless parameters of the fastest growing mode. The results confirm and extend Wardle’s linear analysis.