Interaction of galactic wind with halo gas and the origin of multiphase extraplanar material

Abstract

We study the interaction of a galactic wind with hot halo gas using hydrodynamical simulations. We find that the outcome of this interaction depends crucially on the wind injection density and velocity. Various phases of extraplanar media such as infalling clouds, outflowing clouds and O vi regions can originate in the interaction zones of wind with the halo gas, depending on the injection velocity and density. In our simulations, the size of the clouds is of the order of 100 pc. The total mass contained in the clouds is 105–107 M⊙ and they have a normal distribution of velocities in the galactic standard of rest frame. For high injection density and velocity, a significant number of clouds move outwards and resemble the case of cold neutral outflows. Furthermore, a 105–106 K phase is formed in our simulations, which has a column density ∼1018 cm−2 and resembles the observed O vi regions. The injection velocity and density are linked with the mass-loading factor of the outflow, efficiency of energy injection due to supernovae and star-formation rate. Comparison of the predicted morphology of extraplanar gas with observations can serve as a useful diagnostic for constraining the feedback efficiency of outflows.