Unraveling the origin of magnetic fields in galaxies

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.
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