Supernova Explosions and the Triggering of Galactic Fountains and Outflows

We review here the effects of supernovae (SNe) explosions on the environment of star-forming galaxies. Randomly distributed, clustered SNe explosions cause the formation of hot superbubbles that drive either galactic fountains or supersonic winds out of the galactic disk. In a galactic fountain, the ejected gas is re-captured by the gravitational potential and falls back onto the disk. From 3D non-equilibrium radiative cooling hydrodynamical simulations of these fountains, we find that they may reach altitudes smaller than 5 kpc in the halo and hence explain the formation of the so-called intermediate-velocity-clouds (IVCs). On the other hand, the high-velocity-clouds (HVCs) that are observed 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 out to the halo with the gas in the fountains. Due to angular momentum losses (of 10-15%) to the halo, we find that the fountain material falls back to smaller radii and is not largely spread over the galactic disk, as previously expected. This result is consistent with the metal distribution derived from recent chemical models of the galaxy. We also find that after about 150 Myr, the gas circulation between the halo and the disk in the fountains reaches a steady state regime (abridged).
9 pages, 7 figures, invited paper accepted to: "Magnetic Fields in the Universe II: from Laboratory and Stars to the Primordial Structures", RevMexAA