Dynamo action in spiral galaxies
Inter-University Center for Astronomy and Astrophysics, Pune, Inde
Large-scale magnetic fields in disk galaxies, visible in polarized synchrotron emission and its Faraday rotation, require a generation mechanism that orders magnetic fields on scales larger than the turbulent scale; what is referred to as a mean-field dynamo. In many cases, these fields exhibit deviations from axial symmetry, in particular where the large-scale field is enhanced in spiral magnetic arms akin to, but sometimes phase-shifted from, the optical spiral arms. We present mean-field galactic dynamo models which include non-linear effects arising from magnetic helicity balance (the dynamical alpha-quenching), the delayed response of the mean electromotive force to variations of the mean magnetic field and turbulence parameters (the temporal non-locality), galactic outflows, and realistic spiral structure and evolution. In particular, we isolate three important physical effects which apparently contribute to the formation of magnetic arms.
Date: Jeudi, le 17 avril 2014 Heure: 11:30 Lieu: Université de Montréal Pavillon Roger-Gaudry, local D-460 Contact: Paul Charbonneau