Symmetry and direction of seed magnetic fields in galaxies

Radio observations of large-scale magnetic fields in spiral galaxies suggest that these fields show in many cases a dominating S0 symmetry, i.e. even symmetry to the central plane and axisymmetry with respect to the rotational axis. In addition, detailed evaluation of Faraday rotation measures in five nearby galaxies reveals that in four cases the magnetic field lines are directed toward the centre of these galaxies. Dynamo theory, successful in explaining the existence of such fields, does not contain any statement concerning the sign of the field which depends on the initial conditions. Hence we investigate whether there is a mechanism which produces seed fields with a definitely determined field direction. Neither pre-galactic seed fields, nor galactic battery seed fields, nor ionization fronts are able to imprint such a dominating direction.