Department of Physics, Engineering Physics & Astronomy

Department of Physics, Engineering Physics & Astronomy
Department of Physics, Engineering Physics & Astronomy

Dynamo action in spiral galaxies

Luke Chamandy
The inter-University Centre for Astronomy and Astrophysics

Fri., April 4, 2014
1:30 PM @ Stirling Hall, Theatre A

Abstract:

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 α-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.