3-DIMENSIONAL DYNAMOS IN SPIRAL GALAXIES

Solutions of the 3D nonlinear induction equation for dynamos in spiral galaxies are presented in this paper. Our model includes differential rotation, ambipolar diffusion and, based on small-scale turbulence, e ddy diffusivity and the tensorial alpha-effect underlying magnetic fee dback. The nonaxisymmetric radial-azimuthal spiral pattern and the ver tical stratification of the galaxy are represented in the density and turbulence profile. Our calculations are chiefly concerned with the ef fect of field concentration between (or within) the spiral arms. The p ossible induction of bisymmetric instead of axisymmetric structured fi elds is also investigated. We distinguish between models with weak and strong turbulence contribution, that is small and large correlation t ime tau(corr) of interstellar turbulence. For small correlation times we find axisymmetric steady solutions of even parity showing concentra tion between the spiral arms. The pitch angles are relatively large an d increase with enlarged correlation time. Large correlation times are linked with oscillating BSS type solutions of again even parity, but they are clearly concentrated within the spiral arms.