Jets and multi-phase turbulence .

Abstract

Jets are observed to stir up multiphase turbulence in the interstellar medium as well as far beyond the host galaxy. Here we present detailed simulations of this process. We evolve the hydrodynamics equations with optically thin cooling for a 3D Kelvin Helmholtz setup with one initial cold cloud. The cloud is quickly disrupted, but the fragments remain cold and are spread throughout our simulation box. A scale free isotropic Kolmogorov power spectrum is built up first on the large scales, and reaches almost down to the grid scale after the simulation time of ten million years. We find a pronounced peak in the temperature distribution at 14,000K. The luminosity of the gas in this peak is correlated with the energy. We interpret this as a realisation of the shock ionisation scenario. The interplay between shock heating and radiative cooling establishes the equilibrium temperature. This is close to the observed emission in some Narrow Line Regions. We also confirm the shift of the phase equilibrium, i.e. a lower (higher) level of turbulence produces a higher (lower) abundance of cold gas. The effect could plausibly lead to a high level of cold gas condensation in the cocoons of extragalactic jets, explaining the so called Alignment Effect.