open access

https://hdl.handle.net/2115/66595

Magnetic field evolution and reversals in spiral galaxies

英語

galaxies: magnetic fields

2016-07-07

Oxford University Press

Monthly Notices of the Royal Astronomical Society

461(4)

4482-4495

We study the evolution of galactic magnetic fields using 3D smoothed particle magnetohydrodynamics (SPMHD) simulations of galaxies with an imposed spiral potential.We consider the appearance of reversals of the field, and amplification of the field. We find that magnetic field reversals occur when the velocity jump across the spiral shock is above ?20 km s?1, occurring where the velocity change is highest, typically at the inner Lindblad resonance in our models. Reversals also occur at corotation, where the direction of the velocity field reverses in the corotating frame of a spiral arm. They occur earlier with a stronger amplitude spiral potential, and later or not at all with weaker or no spiral arms. The presence of a reversal at radii of around 4-6 kpc in our fiducial model is consistent with a reversal identified in the Milky Way, though we caution that alternative Galaxy models could give a similar reversal. We find that relatively high resolution, a few million particles in SPMHD, is required to produce consistent behaviour of the magnetic field. Amplification of the magnetic field occurs in the models, and while some may be genuinely attributable to differential rotation or spiral arms, some may be a numerical artefact.We check our results using ATHENA, finding reversals but less amplification of the field, suggesting that some of the amplification of the field with SPMHD is numerical.

学術雑誌論文

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This article has been accepted for publication in Monthly notices of the royal astronomical society © 2016 The Authors Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved.

0035-8711

1365-2966