On the spatial and temporal non-locality of dynamo mean-field effects in supersonic interstellar turbulence

Abstract

The interstellar medium of the Milky Way and nearby disk galaxies harbours large-scale coherent magnetic fields of Microgauss strength, that can be explained via the action of a mean-field dynamo. As in our previous work, we aim to quantify dynamo effects that are self-consistently emerging in realistic direct magnetohydrodynamic simulations, but we generalise our approach to the case of a non-local (non-instantaneous) closure relation, described by a convolution integral in space (time). To this end, we leverage our comprehensive simulation framework for the supernova-regulated turbulent multi-phase interstellar medium. By introducing spatially (temporally) modulated mean fields, we extend the previously used test-field method to the spectral realm -- providing the Fourier representation of the convolution kernels. The resulting spectra of the dynamo mean-field coefficients that we obtain broadly match expectations and allow to rigorously constrain the degree of scale separation in the Galactic dynamo. A surprising result is found for the diamagnetic pumping term, which increases in amplitude when going to smaller scales. Our results amount to the most comprehensive description of dynamo mean-field effects in the Galactic context to date. Surveying the relevant parameter space and quenching behaviour, this will ultimately enable the development of assumption-free sub-grid prescriptions for otherwise unresolved global galaxy simulations.

9 pages, 11 figures, accepted for publication in MNRAS

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Cited by in corpus (8)

• Galactic Dynamos
• Small-Scale Dynamo in Supernova-Driven Interstellar Turbulence
• Finite-time response of dynamo mean-field effects in magnetorotational turbulence
• Non-locality of the Turbulent Electromotive Force
• Mean fields and fluctuations in compressible magnetohydrodynamic flows
• Spatio-temporal non-localities in a solar-like mean-field dynamo
• Turbulent radiative diffusion and turbulent Newtonian cooling
• Investigating global convective dynamos with mean-field models: full spectrum of turbulent effects required