Interstellar medium simulations

Abstract

In this review we critically assess numerical simulations of the interstellar medium (ISM), and argue that 3D high resolu- tion calculations are the most promising method to determine the structure of the interstellar gas and follow its evolution well into the nonlinear regime. Based on a Riemann solver adaptive mesh refinement code, we present a model, which fulfills the basic requirements of running it sufficiently long in order to erase memory effects of the initial conditions,up a disk-halo fountain flow cycle, for converging solutions with increasing mesh refinement. We obtain the following results: (i) in a supernova driven ISM, high Reynolds number turbulence generates structures on all scales, (ii) the volume filling factor of the hot gas is substantially reduced due to the fountain flow, (iii) gas clouds are transient shock compressed layers, (iv) more than half of the gas mass resides in thermally unstable regimes, (v) O VI is distributed in patchy mixing layers, with the derived column densities being in agreement with FUSE and Copernicus observations, (vi) the electron density distribution up to distances of 8 kpc in the disk is consistent with pulsar dispersion measure observations,vided that the electron and ionization structure are not in equilibrium, (vii) the interstellar cooling function dependson space and time (and not only on temperature and metallicity), (viii) the Local Bubble has been produced by 14–20 supernovae about 14 Myr ago, exploding in a moving group on its path through the local ISM, (ix) the nearest supernova explosion to Earth occurred 2.2×106 yr ago at a distance of ∼85 pc, in agreement with measurements of the radionuclide ^60Fe found in the ferromanganese crust on the ocean floor.