I discuss anew how arguments about the internal dynamics of galactic disks set constraints on the otherwise ambiguous decomposition of the rotation curves of spiral galaxies into the contributions by the various constituents of the galaxies. Analyzing the two sample galaxies NGC 3198 and NGC 2985 I conclude from the multiplicities of the spiral arms and the values of the Q disk stability parame...

New high resolution, high sensitivity WSRT H i synthesis observations of the spiral galaxy NGC 3631 are presented. In the total atomic hydrogen map, the spiral arms are well distinguished from the interarm regions, while the sensitivity allows detection of H i in all but a few isolated regions of the areas between the spiral arms. Most of the atomic hydrogen is located within the optical disc, ...

Dynamo models for the structure of the regular magnetic field in the galaxy NGC 6946 are confronted with recent observations of polarized radio emission at λ3.5 cm. The observed behaviour of the concentration of regular fields between the gaseous spiral arms (“magnetic spiral arms”) is achieved via a non-axisymmetric azimuthal distribution of only the correlation time τcorr of interstellar turb...