Magnetic Fields and Mass Inflow in Central Regions of Barred Galaxies

Radio continuum emission is an excellent tracer of star formation in central regions of galaxies. We observed a sample of 20 galaxies with massive bars. The regular magnetic fields around the bar, as traced by the polarized emission, do not always follow the gas flow predicted from numerical simulations and show little compression by the shock. The galaxies with the longest bars show the strongest deviations of the magnetic field pattern from axial symmetry, and most of them host nuclear rings. The total magnetic fields in these nuclear rings of up to 100 muG are among the strongest fields known in spiral galaxies. The regular field in the nuclear ring of NGC 1097 is of spiral shape. Magnetic stress in the ring can drive mass inflow of about one solar mass per year which is sufficient to feed the active nucleus. This process may also work in non-barred galaxies.