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Galactic fountains are thought to be responsible for the formation of the observed intermediate and high velocity clouds in the Galactic halo. Threedimensional simulations have been carried out to determine the evolution of the disk gas as it enters the fountain, cools and returns to the Galactic disk. The descending cold gas, headed by a shock, sweeps up the ascending flow, triggering the formation...
The intercloud medium (ICM) is kept hot and supplied with gas by supernova remnants of Type II. The rate at which mass is added balances the rate at which gas flows away from the ICM into the galactic halo. A fountain is thus formed, since the gas only has enough energy to escape from the disk, but not from the Galaxy as a whole. The upward flow must be followed by the descent of the gas, in the form...
Turbulent mixing between an ionization bounded HII region and a hot shocked stellar wind (HSSW), which keeps it under pressure, is examined. Recently we have shown that acoustic disturbances can grow there to finite amplitude in a time scale which is comparable to the sound crossing time in the HII layer. The resulting turbulence will then stretch fluid elements and the frozen-in magnetic field. A...
Intermediate and high velocity clouds are produced in a Galactic fountain as a result of Rayleigh-Taylor instabilities that grow at the interface separating the cool descending gas and the hot ascending gas within the fountain flow. It is proposed here that there is no need to introduce any initial perturbation to the system in order to trigger such instabilities. They will arise naturally as a result...
The Galactic fountain is driven by the hot inter-cloud medium (ICM). The ICM itself is heated by successive supernova explosions. This process introduces sufficient irregularities to prevent the fountain flow from being smooth. Instead it leads to the formation of a frothy medium above the disk (Avillez, Berry & Kahn 1997). This paper describes the effect of successive supernova explosions, in...