Unusual magnetic fields in the interacting spiral NGC 3627

By observing the interacting galaxy NGC 3627 in radio polarization we try t o answer the question; to which degree does the magnetic field follow the g alactic gas ow. We obtained total power and polarized intensity maps at 8.4 6 GHz and 4.85 GHz using the VLA in its compact D-configuration. In order t o overcome the zero-spacing problems, the interferometric data were combine d with single-dish measurements obtained with the Effelsberg 100-m radio te lescope. The observed magnetic field structure in NGC 3627 suggests that tw o field components are superposed. One component smoothly fills the interar m space and shows up also in the outermost disk regions, the other componen t follows a symmetric S-shaped structure. In the western disk the latter co mponent is well aligned with an optical dust lane, following a bend which i s possibly caused by external interactions. However, in the SE disk the mag netic field crosses a heavy dust lane segment, apparently being insensitive to strong density-wave effects. We suggest that the magnetic field is deco upled from the gas by high turbulent diffusion, in agreement with the large Hi line width in this region. We discuss in detail the possible influence of compression effects and non-axisymmetric gas flows on the general magnet ic field asymmetries in NGC 3627. On the basis of the Faraday rotation dist ribution we also suggest the existence of a large ionized halo around this galaxy.