Unraveling the origin of magnetic fields in galaxies

TL;DR

This study investigates whether primordial magnetic fields can be distinguished from astrophysical sources in galaxies by simulating different magnetisation scenarios and analyzing magnetic signatures across cosmic time.

Contribution

The paper introduces a magnetic tracers algorithm to identify primordial magnetic field signatures in galaxies, demonstrating their dominance when above a certain strength and proposing observational methods to differentiate their origins.

Findings

Primordial magnetic fields with B0 > 10^{-12} G dominate galaxy magnetisation.

Magnetic signatures of primordial fields persist in the warm metal-poor phase.

Future observations can distinguish between primordial and astrophysical magnetic sources.

Abstract

Despite their ubiquity, there are many open questions regarding galactic and cosmic magnetic fields. Specifically, current observational constraints cannot rule out if magnetic fields observed in galaxies were generated in the Early Universe or are of astrophysical nature. Motivated by this we use our magnetic tracers algorithm to investigate whether the signatures of primordial magnetic fields persist in galaxies throughout cosmic time. We simulate a Milky Way-like galaxy in four scenarios: magnetised solely by primordial magnetic fields, magnetised exclusively by SN-injected magnetic fields, and two combined primordial + SN magnetisation cases. We find that once primordial magnetic fields with a comoving strength $B_0 >10^{-12}$ G are considered, they remain the primary source of galaxy magnetisation. Our magnetic tracers show that, even combined with galactic sources of magnetisation, when primordial magnetic fields are strong, they source the large-scale fields in the warm metal-poor phase of the simulated galaxy. In this case, the circumgalactic and intergalactic medium can be used to probe $B_0$ without risk of pollution by magnetic fields originated in the galaxy. Furthermore, whether magnetic fields are primordial or astrophysically-sourced can be inferred by studying local gas metallicity. As a result, we predict that future state-of-the-art observational facilities of magnetic fields in galaxies will have the potential to unravel astrophysical and primordial magnetic components of our Universe.