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Lookup NU author(s): Yasin Qazi, Professor Anvar ShukurovORCiD, Dr Devika Tharakkal, Dr Fred Gent
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.Magnetic buoyancy (MBI) and Parker instabilities are strong, generic instabilities expected to occur in most astrophysical systems with sufficiently strong magnetic fields. In galactic and accretion discs, large-scale magnetic fields are thought to arise from mean-field dynamo action, particularly the $/alpha ^2/Omega$-dynamo. Using non-ideal MHD equations, we model a section of the galactic disc where the large-scale magnetic field is generated by an imposed $/alpha$-effect and differential rotation. We extend our previous study of the interplay between magnetic buoyancy and the mean-field dynamo by incorporating differential rotation, which enhances the dynamo, and cosmic rays, which amplify magnetic buoyancy. We construct a simple one-dimensional (1D) model which replicates all significant features of the three-dimensional (3D) simulations. Simulations confirm that magnetic buoyancy can lead to oscillatory magnetic fields and reveal that it can change the magnetic field parity between quadrupolar and dipolar states. Differential rotation facilitates this switch in parity, suggesting that the large-scale magnetic field can adopt a dipolar parity within a few kiloparsecs of the galactic centre. In contrast, quadrupolar parity may remain predominant in the outer parts of a galactic disc. Cosmic rays accelerate both the dynamo and the MBI, supporting oscillatory non-linear states and a spatial magnetic field structure similar to the alternating magnetic field directions observed in the haloes of some edge-on galaxies.
Author(s): Qazi Y, Shukurov A, Tharakkal D, Gent FA, Bendre AB
Publication type: Article
Publication status: Published
Journal: Monthly Notices of the Royal Astronomical Society
Year: 2025
Volume: 540
Issue: 1
Pages: 532-544
Print publication date: 01/06/2025
Online publication date: 14/05/2025
Acceptance date: 05/05/2025
Date deposited: 02/06/2025
ISSN (print): 0035-8711
ISSN (electronic): 1365-2966
Publisher: Oxford University Press
URL: https://doi.org/10.1093/mnras/staf766
DOI: 10.1093/mnras/staf766
Data Access Statement: The raw data for this work were obtained from numerical simulations using the open source PENCIL-CODE available at https://github .com/pencil-code/pencil-code.git. The derived data used for the analysis are available from the corresponding author on a reasonable request.
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