GALACTIC DYNAMICS AND GALACTIC DYNAMOS - EVIDENCE FOR A BOND

Dynamical processes, such as tidal interactions, can have a profound influence on the magnetic field structure in galactic disks. Very few galaxies lived quiescent existences. Traces of past dynamical activities of a spiral galaxy may be found in the shape of its neutral hydrogen (H I) gas distribution, in the form of morphological deformations (MD). Thus fossil H I gas may point a finger towards a passing neighbor galaxy. Galactic dynamo states of spiral galaxies can be found in the shape of the global magnetic field distribution, more generally in its azimuthal mode (m(azim)). Global magnetic modes can be axisymmetric or bisymmetric. Here, MD examples are obtained for NGC 891, NGC 4631, and the Large Magellanic Cloud (LMC), for which m(azim) has recently been suggested. Also, I find many observational evidence to link statistically galactic dynamos and galactic dynamics, via their parameters m(azim) and MD. A more complex H I morphological shape (MD value) goes along with a more complex magnetic field shape (m(azim) value), and vice-versa, e.g. Table 2 and Fig. 5. This statistical link points to a necessary common cause for creating H I fossils and global magnetic shapes, ie most likely a deformed gravitational potential around a spiral galaxy. The deformation of the galactic gravitational potential may be caused by a tidal encounter with a nearby companion galaxy, or by a long rotating bar straddling the galactic nucleus. Such a deformed gravitational potential would require new terms in the general dynamo equations employed to date for galactic magnetism. The time-evolution of the deformed gravitational potential could be the main trigger to change the m(azim) from axisymmetric (0), to bisymmetric (I), and vice-versa.