This work demonstrates that the Biermann battery effect is expected to produce weak, large scale, magnetic fields during the collapse of proto-galactic objects in a very natural fashion. A semi-analytic model is developed that allows the initial geometry and strength of these fields to be estimated. Here we find the vorticity scale is simply set by the collapse time of the object, and that the corresponding magnetic seed field for galaxy sized objects is of order 10-20G, which, after compression into the galactic disk, will be of sufficient strength to be a good candidate to seed the galactic dynamo. Numerical simulations are then used to verify and augment these semi-analytic results, and to determine how accurately SPH methods can actually measure vorticity. The results here indicate that the overall features of the semi-analytic model are well corroborated by the numerics, but that some of the finer structures can not yet be reliably resolved. Though this is not a fundamental limitation of the approach, and future work should be able to provide better resolution.
- Pub Date:
- December 2002
- Physics: Astronomy and Astrophysics