Galactic fountains and gas accretion

Star-forming disc galaxies such as the Milky Way need to accrete > ∼ 1 M⊙ of gas each year to sustain the process of 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 a similar mass of 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.