GALACTIC DYNAMICS AND GALACTIC DYNAMOS - EVIDENCE FOR A BOND

Dynamical processes, such as tidal interactions, can have a profound i nfluence on the magnetic field structure in galactic disks. Very few g alaxies lived quiescent existences. Traces of past dynamical activitie s 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 g alaxy. Galactic dynamo states of spiral galaxies can be found in the s hape 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, an d the Large Magellanic Cloud (LMC), for which m(azim) has recently bee n suggested. Also, I find many observational evidence to link statisti cally galactic dynamos and galactic dynamics, via their parameters m(a zim) and MD. A more complex H I morphological shape (MD value) goes al ong 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 nec essary common cause for creating H I fossils and global magnetic shape s, ie most likely a deformed gravitational potential around a spiral g alaxy. The deformation of the galactic gravitational potential may be caused by a tidal encounter with a nearby companion galaxy, or by a lo ng rotating bar straddling the galactic nucleus. Such a deformed gravi tational potential would require new terms in the general dynamo equat ions employed to date for galactic magnetism. The time-evolution of th e deformed gravitational potential could be the main trigger to change the m(azim) from axisymmetric (0), to bisymmetric (I), and vice-versa .