3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies

Abstract

Star-forming dwarf galaxies can be seen as the local proxies of the high-redshift building blocks of more massive galaxies according to the current paradigm of the hierarchical galaxy formation. They are low-mass objects, and therefore their rotation speed is very low. Several galaxies are observed to show quite strong magnetic fields. These cases of strong ordered magnetic fields seem to correlate with a high, but not extremely high, star formation rate. We investigate whether these magnetic fields could be generated by the cosmic-ray-driven dynamo. The environment of a dwarf galaxy is unfavourable for the large-scale dynamo action because of the very slow rotation that is required to create the regular component of the magnetic field. We built a 3D global model of a dwarf galaxy that consists of two gravitational components: the stars and the dark-matter halo described by the purely phenomenological profile proposed previously. We solved a system of magnetohydrodynamic (MHD) equations that include an additional cosmic-ray component described by the fluid approximation. We found that the cosmic-ray-driven dynamo can amplify the magnetic field with an exponential growth rate. The $e$-folding time is correlated with the initial rotation speed. The final mean value of the azimuthal flux for our models is of the order of few $\mu$G and the system reaches its equipartition level. The results indicate that the cosmic-ray-driven dynamo is a process that can explain the magnetic fields in dwarf galaxies.

6 pages, 4 figures, accepted for publication in A&A

References in corpus (8)

• Numerical Tests of Fast Reconnection in Weakly Stochastic Magnetic Fields
• Simulations of disk galaxies with cosmic ray driven galactic winds
• Direct simulations of a supernova-driven galactic dynamo
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• Galactic Dynamos and Galactic Winds
• Global simulations of the magnetic field evolution under the influence of the cosmic-ray-driven dynamo

Cited by in corpus (15)

• Magnetic Fields in Spiral Galaxies
• Nonthermal particles and photons in starburst regions and superbubbles
• Global diffusion of cosmic rays
• Cosmological simulations of galaxy formation with cosmic rays
• Ab initio Simulations of a Supernova Driven Galactic Dynamo in an Isolated Disk Galaxy
• Simulations of cosmic ray propagation
• Implementation of CR Energy SPectrum (CRESP) algorithm in PIERNIK MHD code. I. Spectrally resolved propagation of CR electrons on Eulerian grids
• The non-thermal superbubble in IC 10: the generation of cosmic ray electrons caught in the act
• The magnetized galactic wind and synchrotron halo of the starburst dwarf galaxy IC10
• Enhancement of magnetic fields arising from galactic encounters
• The supernova-regulated ISM -- VI. Magnetic effects on the structure of the interstellar medium
• Magnetic fields near the peripheries of galactic discs
• Galactic winds and the origin of large-scale magnetic fields
• Magnetic field evolution in dwarf and Magellanic-type galaxies
• Somewhere in between: Tracing the Radio Emission from Galaxy Groups (or Why Does the Future of Observing Galaxy Groups with Radio Telescopes Look Promising?)