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

TL;DR

This study uses hydrodynamical simulations to explore how galactic winds interact with halo gas, producing various multiphase extraplanar structures like high velocity clouds and OVI regions, depending on wind parameters.

Contribution

It demonstrates how wind-halo interactions can generate multiphase extraplanar material, linking simulation results to observed galactic features and feedback processes.

Findings

High velocity clouds have sizes around 100 pc.

Cloud masses range from 10^5 to 10^7 solar masses.

A 10^5-10^6 K phase with column density ~10^{18} cm^{-2} is formed.

Abstract

We study the interaction of 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 the extraplanar media such as high velocity clouds (HVCs), outflowing clouds, and OVI 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 HVCs is of the order of 100 pc. The total mass contained in the clouds is 10^5 -- 10^7 M_sun and they have a normal distribution of velocities in the galactic standard of rest frame, similar to HVCs. For high injection density and velocity, a significant number of clouds move outwards and resemble the case of cold neutral outflows. Furthermore a 10^5 -- 10^6 K phase is formed in our simulations which has a column density ~ 10^{18} cm^{-2}, and resembles the observed OVI regions. The injection velocity and density are linked with the mass loading factor of the outflow, efficiency of energy injection due to supernovae and the SFR. Comparison of the predicted morphology of extraplanar gas with observations can serve as a useful diagnostic for constraining feedback efficiency of outflows.