Magnetic field evolution and reversals in spiral galaxies

Abstract

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 magnetic field reversals occur when the velocity jump across the spiral shock is above $\approx$20km s${}^{-1}$, occurring where the velocity change is highest, typically at the inner Lindblad resonance (ILR) in our models. Reversals also occur at corotation, where the direction of the velocity field reverses in the co-rotating 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 a 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.

15 pages, 13 figures, accepted for publication in MNRAS

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Cited by in corpus (7)

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• A guided map to the Spiral arms in the galactic disk of the Milky Way
• Local simulations of MRI turbulence with meshless methods
• Global enhancement and structure formation of the magnetic field in spiral galaxies
• The role of previous generations of stars in triggering star formation and driving gas dynamics
• Superposing the Magnetic spiral structure of the Milky Way, on the stellar spiral arms -- Matching the unique galactic magnetic field reversal Zone with two galactic spiral arm Segments
• Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges