Evolution of the Turbulent Interstellar Medium in Star Forming Galaxies

The evolution of galaxies is driven by the continuous formation of
stars out of interstellar matter (ISM). The ISM is a highly
compressible and magnetized medium, characterized by Reynolds numbers,
exceeding those in most terrestrial laboratories by orders of
magnitude. Supernova (SN) explosions and stellar winds of massive
stars are the dominant sources of kinetic energy in the ISM. Thus
shear flows generate a high level of vorticity, leading to a very
turbulent medium.  The inherent complexity and nonlinearity of the
system require a careful approach, especially for advanced numerical
3D parallel computer simulations. We have built a bottom-up model of a
turbulent SN driven ISM over the years, showing (amongst others) by
large scale hydro- and magnetohydrodynamical simulations (i) the
existence of a large scale galactic fountain, (ii) a reduced volume
filling factor of hot gas, and (iii) a considerable fraction of the
gas mass residing in classical thermally unstable phases. In addition,
we have recently calculated the fully time-dependent ionization
structure for the 10 most abundant elements along with the
hydrodynamics.  Since the plasma is generally out of ionization
equilibrium, the cooling function is varying both in space and time,
depending on the thermal history of the plasma.  The simulations are
compared to some recent observations, and prospects of current and
future work are discussed.