The dynamical signature of the ISM in soft X-rays - I. Diffuse soft X-raysfrom galaxies

We present the first dynamically and thermally self-consistent calculations of fast adiabatically expanding gas flows from the Galactic disk into the halo. It is shown that in a hot plasma (T greater than or equal to 10(6) K) with a high overpressure with respect to the ambient medium, the dynamical time scale is much shorter than the intrinsic time scales (e.g. for recomb ination, collisional excitation and ionization etc.). Therefore dynamical m odels that use collisional ionization equilibrium (CIE) cooling functions f or the evolution of the plasma are in general not correct. In particular, t he emission spectra obtained from non-equilibrium calculations are radicall y different. We describe a method to obtain self-consistent solutions using an iterative procedure. It is demonstrated that soft X-ray background emis sion between 0.3 and 1.5 keV can be well explained by a superposition of li ne emission and delayed recombination of an initially hot plasma streaming away from the Galactic disk (outflow and/or winds). In addition to these lo cal winds we also present calculations on global winds from spiral galaxies , which originate from a hot and quiescent galactic corona. We also emphasi ze that it is dangerous to derive plasma temperatures merely from line rati os of ionized species, such as N v/O vI, unless the dynamical and thermal h istory of the plasma is known.