The Non-linear Thin Shell Instability in Cloud-Cloud Collisions

Supersonic cloud-cloud collisions will produce a dense, shock-confined layer. This layer may be unstable to the non-linear thin shell instability (NTSI). We first explore the effect of different initial perturbations on the growth of the NTSI using smoothed particle hydrodynamics (SPH) simulations. We use one-dimensional monochromatic perturbations. We also use subsonic and supersonic turbulence to trigger the NTSI. We show partial agreement with the analytic predictions of Vishniac (ApJ 428:186, 1994). We then simulate a more realistic supersonic collision of molecular clouds with internal subsonic turbulence at a range of collision velocities. We show that at low collision velocity gravitational instability is dominant, but at higher collision velocities the NTSI becomes dominant and eventually suppresses star formation.