The formation of molecular clouds: The origin of supersonic turbulence

We have done two- and three-dimensional magnetohydro-dynamical simulations of the propagation of a, shock wave into the interstellar medium by taking into account radiative heating/cooling, thermal conduction, and physical viscosity. Our results show that the thermal instability in the post-shock gas in the interstellar medium produces high-density molecular cloudlets which have a supersonic velocity dispersion. The dynamical evolution driven by thermal instability in the post-shock layer is an important basic process for the transition from warm gases to cold molecular gases, because the shock waves are frequently generated by supernovae in the Galaxy.