On the generation of bisymmetric magnetic field structures in spiral galaxies by tidal interactions

Abstract

Tidal interactions involving spiral galaxies are expected to drive non-axisymmetric gas motions in their discs. After reducing the linear mean field dynamo equations to two spatial dimensions by removing the explicit dependence on the distance from the disc plane, the effects of such motions on the excitation of bisymmetric magnetic fields are investigated. It is found that an m = 2 velocity component of physically realistic magnitude can preferentially excite an m = 1 magnetic field in this strictly linear model. It is emphasized that results from linear theory may be an unreliable guide to behaviour in the non-linear regime.