Galactic Outflows and the pollution of the Galactic Environment by Supernovae

TL;DR

This paper investigates how supernova explosions in star-forming galaxies create hot superbubbles that drive galactic fountains and winds, influencing halo clouds, gas recycling, and chemical enrichment.

Contribution

It provides 3D hydrodynamical simulations showing the formation of galactic fountains, their altitude limits, and implications for halo cloud formation and chemical distribution.

Findings

Fountains reach up to 5 kpc, forming intermediate-velocity clouds.

High-velocity clouds may form from intergalactic gas or magnetic fields.

Ejected material mostly falls back near the original region, affecting galaxy chemistry.

Abstract

We here explore the effects of the SN explosions into the environment of star-forming galaxies like the Milky Way. Successive randomly distributed and clustered SNe explosions cause the formation of hot superbubbles that drive either fountains or galactic winds above the galactic disk, depending on the amount and concentration of energy that is injected by the SNe. In a galactic fountain, the ejected gas is re-captured by the gravitational potential and falls back onto the disk. From 3D nonequilibrium radiative cooling hydrodynamical simulations of these fountains, we find that they may reach altitudes up to about 5 kpc in the halo and thus allow for the formation of the so called intermediate-velocity-clouds (IVCs) which are often observed in the halos of disk galaxies. The high-velocity-clouds that are also observed but at higher altitudes (of up to 12 kpc) require another mechanism to explain their production. We argue that they could be formed either by the capture of gas from the intergalactic medium and/or by the action of magnetic fields that are carried to the halo with the gas in the fountains. Due to angular momentum losses to the halo, we find that the fountain material falls back to smaller radii and is not largely spread over the galactic disk. Instead, the SNe ejecta fall nearby the region where the fountain was produced, a result which is consistent with recent chemical models of the galaxy. The fall back material leads to the formation of new generations of molecular clouds and to supersonic turbulence feedback in the disk.