Galactic fountains and gas accretion

TL;DR

This paper uses simulations to demonstrate that cold galactic-fountain clouds can induce cooling and accretion of hot coronal gas, supporting the process needed for star formation in galaxies like the Milky Way.

Contribution

It provides the first detailed simulation evidence that galactic-fountain clouds trigger coronal gas cooling and accretion, explaining how galaxies sustain star formation.

Findings

Simulations show clouds strip gas via Kelvin-Helmholtz instability.

Stripped gas induces condensation of coronal gas in cloud wakes.

Resulting accretion rate matches star formation needs.

Abstract

Star-forming disc galaxies such as the Milky Way need to accrete $\gsim$ 1 $M_{\odot}$ of gas each year to sustain their star formation. This gas accretion is likely to come from the cooling of the hot corona, however it is still not clear how this process can take place. We present simulations supporting the idea that this cooling and the subsequent accretion are caused by the passage of cold galactic-fountain clouds through the hot corona. The Kelvin-Helmholtz instability strips gas from these clouds and the stripped gas causes coronal gas to condense in the cloud's wake. For likely parameters of the Galactic corona and of typical fountain clouds we obtain a global accretion rate of the order of that required to feed the star formation.