A small-scale dynamo in feedback-dominated galaxies - III. Cosmological simulations

TL;DR

This paper presents a high-resolution cosmological MHD simulation demonstrating how weak initial magnetic fields in dwarf galaxies are rapidly amplified by a small-scale dynamo driven by supernova turbulence, influencing cosmic magnetism.

Contribution

It introduces a novel cosmological simulation showing the amplification of magnetic fields via a small-scale dynamo in feedback-dominated galaxies, with implications for high-redshift magnetic field structures.

Findings

Magnetic fields are amplified rapidly in early dwarf galaxies.

Small-scale dynamo dominates magnetic field growth in turbulent environments.

High-redshift magnetic fields are likely dominated by small-scale components.

Abstract

Magnetic fields are widely observed in the Universe in virtually all astrophysical objects, from individual stars to entire galaxies, even in the intergalactic medium, but their specific generation has long been debated. Due to the development of more realistic models of galaxy formation, viable scenarios are emerging to explain cosmic magnetism, thanks to both deeper observations and more efficient and accurate computer simulations. We present here a new cosmological high-resolution zoom-in magnetohydrodynamic (MHD) simulation, using the adaptive mesh refinement (AMR) technique, of a dwarf galaxy with an initially weak and uniform magnetic seed field that is amplified by a small-scale dynamo driven by supernova-induced turbulence. As first structures form from the gravitational collapse of small density fluctuations, the frozen-in magnetic field separates from the cosmic expansion and grows through compression. In a second step, star formation sets in and establishes a strong galactic fountain, self-regulated by supernova explosions. Inside the galaxy, the interstellar medium becomes highly turbulent, dominated by strong supersonic shocks, as demonstrated by the spectral analysis of the gas kinetic energy. In this turbulent environment, the magnetic field is quickly amplified via a small-scale dynamo process and is finally carried out into the circumgalactic medium by a galactic wind. This realistic cosmological simulation explains how initially weak magnetic seed fields can be amplified quickly in early, feedback-dominated galaxies, and predicts, as a consequence of the small scale dynamo process, that high-redshift magnetic fields are likely to be dominated by their small scale components.