Accretion and galactic dynamos

We show that radial flows (directed either inward or outward) suppress mean-field dynamo action in a thin disc. Under conditions typical of spiral galaxies, the reduction in the growth rate of the large-scale magnetic field can reach 25-30%. The dynamo-generated galactic magnetic fields themselves can drive radial flows at a rate of order 0.1 M(.)yr(-1). These radial flows can contribute to the saturation of the dynamo action together with other nonlinear effects. We also present arguments, and an illustrative computation, to support the view that in the inner regions of barred galaxies the magnetically driven mass accretion rate may be substantially larger than the above estimate due to deviations of magnetic field from axial symmetry. The magnetically driven inflow rate in barred galaxies can reach about 3 M(.)yr(-1).