MAGNETIC HEATING OF THE GALACTIC HALO

A numerical model for the heating of the boundaries of high-velocity c louds (HVC) falling onto the galactic disk is presented. X-ray observa tions reveal temperatures of a few million Kelvin, In order to reach t he observed temperatures the whole kinetic energy of the clouds has to be transformed into thermal plasma energy. So, a mechanism effectivel y braking the clouds has to be assumed. We propose magnetic reconnecti on as the braking agent: During the impact of a HVC onto the galactic halo the magnetised plasma becomes turbulent and magnetic field lines of different polarity approach each other. Outside the forming current sheets the magnetic field lines are frozen in as a consequence of the high electrical conductivity of the plasma, Inside the sheets the cur rent density grows and excites microscopic turbulences leading to loca lized collective resistivity. Three dimensional numerical MHD-simulati ons are performed to calculate the corresponding heating rates.