Magnetic Field Structure of the Galaxy and the Formation of Galactic Winds

Abstract

Using the basic observational characteristics of the interstellar galactic cosmic ray component, a plausible large-scale magnetic field structure above the gaseous disk of the Galaxy is described. To a considerable extent the field lines should be perpendicular to the galactic disk at heights exceeding several kiloparsec and open towards intergalactic space. This allows cosmic ray loss from the Galaxy, which is largely convective for the lower energy part of the particle spectrum dominating the cosmic ray pressure. The negative outwards cosmic ray pressure gradient gives rise to self-excited MHD-waves due to the streaming instability. As a consequence cosmic ray and wave pressures can drive a galactic mass loss against the gravitational pull of the disk and a massive and extended halo. A typical solution for an adiabatic wind is presented. Obvious areas for observational tests should be the synchrotron structure of galactic halos, as well as spectroscopy of highly ionized species in the UV and soft X-ray regions.