A steady density wave in a disc-like galaxy could lead to a spiral form for the crucial α-effect term in standard dynamo theory. We had earlier studied this problem under the thin-disc approximation and by effecting an approximate separation of variables between the z-dependence and the r, ϕ-dependences of the magnetic field. We return to this problem by making an alternative approximation of our equations, which allows a better treatment of the case of strong departures from axisymmetry, albeit with a cruder treatment of the z-dependence. The numerical solution of the equations reveals, as in our earlier work, the existence of rapidly growing, global, bisymmetric magnetic modes, corotating with the density wave. The modes extend several kiloparsecs around the radius rc where the wave corotates with the gas. The magnetic spiral is closely aligned with the density wave in regions where it has maximum strength; leading within rc and trailing outside. These results are remarkably similar to that obtained in our earlier work, under a very different approximation scheme, encouraging belief in the robustness of the results obtained in both papers.
No takes yet. Share an insight, caveat, or question.
Subramanian et al. (1993) studied this question.