On the Combined Role of Cosmic Rays and Supernova-Driven Turbulence for Galactic Dynamos
arXiv:2010.03654 · doi:10.1093/mnras/staa3509
Abstract
Large-scale coherent magnetic fields observed in the nearby galaxies are thought to originate by a mean-field dynamo. This is governed via the turbulent electromotive force (EMF, ) generated by the helical turbulence driven by supernova (SN) explosions in the differentially rotating interstellar medium (ISM). In this paper we aim to investigate the possibility of dynamo action by the virtue of buoyancy due to a cosmic ray (CR) component injected through the SN explosions. We do this by analysing the magnetohydrodynamic simulations of local shearing box of ISM, in which the turbulence is driven via random SN explosions and the energy of the explosion is distributed in the CR and/or thermal energy components. We use the magnetic field aligned diffusion prescription for the propagation of CR. We compare the evolution of magnetic fields in the models with the CR component to our previous models that did not involve the CR. We demonstrate that the inclusion of CR component enhances the growth of dynamo slightly. We further compute the underlying dynamo coefficients using the test-fields method, and argue that the entire evolution of the large scale mean magnetic field can be reproduced with an dynamo model. We also show that the inclusion of CR component leads to an unbalanced turbulent pumping between magnetic field components and additional dynamo action by the Rädler effect.
arXiv comment9 pages, 5 figures, 1 tables
References in corpus (21)
- Astrophysical magnetic fields and nonlinear dynamo theory
- Strong magnetic fields in normal galaxies at high redshifts
- Launching cosmic-ray-driven outflows from the magnetized interstellar medium
- Dynamo theories
- Magnetic diffusivity tensor and dynamo effects in rotating and shearing turbulence
- Electromotive Force and Large-Scale Magnetic Dynamo in a Turbulent Flow with a Mean Shear
- Direct simulations of a supernova-driven galactic dynamo
- Global galactic dynamo driven by cosmic-rays and exploding magnetized stars
- Amplification of Galactic Magnetic Fields by the Cosmic-Ray Driven Dynamo
- Advances in mean-field dynamo theory and applications to astrophysical turbulence
- Anisotropic CR diffusion and gamma-ray production close to supernova remnants, with an application to W28
- The Effect of Cosmic Ray Diffusion on the Parker Instability
- Cosmic Rays in Intermittent Magnetic Fields
- Dynamo coefficients from local simulations of the turbulent ISM
- Simulating field-aligned diffusion of a cosmic ray gas
- Advances in theory and simulations of large-scale dynamos
- Dynamo saturation in direct simulations of the multi-phase turbulent interstellar medium
- Toward a hybrid dynamo model for the Milky Way
- Cosmic-ray driven dynamo in the interstellar medium of irregular galaxies
- On the magnetic quenching of mean-field effects in supersonic interstellar turbulence
- Magnetic fields in nearby galaxies