A surprising side of Supernova feedback
Galactic fountain is a mechanism powered by star formation activity in the discs of galaxies that effectively brings gas and dust outside the planes of the discs into the galactic halos. The energy and momentum sources are supernova explosions, mostly in OB associations, the collective contribution of which creates large expanding shells called supershells that reach sizes larger than the typical scaleheigth of galaxy discs, i.e., a few hundreds parsec.


The simulation above shows several snapshots of the temperature distribution in a hydrodynamical simulation of a fountain cold cloud leaving the galactic plane (at z=0, bottom of the panels) and traveling through the corona. The interaction with the hot medium produces a turbulent wake behind the cloud where hot and cold gases mix efficiently. Given the high metallicity of the cold gas (it comes from the star forming disc) this mixing makes the cooling time of the coronal material dropping by a few orders of magnitude. In the end the amount of cold gas in the system cloud+wake increases with time and the fountain brings back to the disc more gas than that that had been ejected from it (Marasco, Fraternali & Binney 2012).
You can find a
movie of a similar simulation here.