LOCALIZED MAGNETIC RECONNECTION AS A CAUSE OF EXTRAPLANAR DIFFUSE IONIZED-GAS IN THE GALACTIC HALO

Many observations indicate the occurrence of ionized gas in the distan t haloes of galaxies (including our own). Since photoionization by sta rs (mainly O stars, young stars or evolved low-mass stars depending on the kind of galaxy) does not seem to be exclusively responsible for t he ionization of the hydrogen filaments that should otherwise cool fas t and recombine quickly, the question arises which extra energy source can produce the quasi-stationary ionization. We show that stationary localized magnetic reconnection in current filaments may contribute to the ionization of the extraplanar halo gas. In these filaments magnet ic energy is dissipated. Consequently, the ionized as well as the neut ral component is heated and re-ionized on a time-scale significantly s horter than the recombination time-scale. The amount of energy require d for efficient re-ionization can in principle easily be provided by t he free magnetic energy. We present quasi-static models that are chara cterized by plasma temperatures and densities that agree well with the observed values for the diffuse ionized gas component of the interste llar medium. Plasma-neutral gas fluid simulations are made to show tha t the recombination-induced dynamical reconnection process indeed work s in a self-regulatory way.