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The origin of the structure of large-scale magnetic fields in disc galaxies

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posted on 2018-06-05, 14:20 authored by C. J. Nixon, T. O. Hands, A. R. King, J. E. Pringle
The large-scale magnetic fields observed in spiral disc galaxies are often thought to result from dynamo action in the disc plane. However, the increasing importance of Faraday depolarization along any line of sight towards the galactic plane suggests that the strongest polarization signal may come from well above (~0.3-1 kpc) this plane, from the vicinity of the warm interstellar medium (WIM)/halo interface. We propose (see also Henriksen & Irwin 2016) that the observed spiral fields (polarization patterns) result from the action of vertical shear on an initially poloidal field. We show that this simple model accounts for the main observed properties of large-scale fields.We speculate as to howcurrent models of optical spiral structure may generate the observed arm/interarm spiral polarization patterns.


CJN is supported by the Science and Technology Facilities Council (STFC) (Grant No. ST/M005917/1). CJN was supported in part by the National Science Foundation under Grant No. NSF PHY-1125915. The Theoretical Astrophysics Group at the University of Leicester is supported by an STFC Consolidated Grant. TOH acknowledges support from the Swiss National Science Foundation Grant No. 200020_162930. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility ( This equipment is funded by BIS National E-Infrastructure capital Grant No. ST/K000373/1 and STFC DiRAC Operations Grant No. ST/K0003259/1. DiRAC is part of the UK National E-Infrastructure. We used SPLASH (Price 2007) for the visualization.



Monthly Notices of the Royal Astronomical Society, 2018, 477 (3), pp. 3539-3551

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