Magnetising galaxies with cold inflows

TL;DR

This paper presents an analytic model showing that cold gas inflows at high redshift can magnetize galaxies to microgauss levels, explaining observed magnetic fields in early galaxies.

Contribution

It introduces a simple analytic model linking cold stream accretion to galactic magnetic field amplification, supported by simulation data.

Findings

Magnetic fields exceeding microgauss levels can be generated by cold inflows at high redshift.

Model predictions align with observed strong magnetic fields in galaxies at z > 2.6.

Cold streams are a viable mechanism for seeding galactic magnetic fields.

Abstract

High-redshift ($z\sim2-3$) galaxies accrete circumgalactic gas through cold streams. Recent high-resolution MHD simulations of these streams showed a significant amplification of the intergalactic magnetic field in the shear layer around them. In this work we estimate the magnetisation of high-redshift galaxies that would result purely due to the accretion of already magnetised gas from cold streams. We use the mass inflow rates and saturated magnetic field values from cold stream simulations as input to a simple analytic model that calculates the galactic magnetic field purely from mass accretion. Our model predicts average magnetic field strengths that exceed $\rm\mu G$ values at $z\sim 2-3$ for inflow rates above $0.1 \, \rm{M_{\odot} yr^{-1}}$. For high inflow rates, our model results are consistent with the recent detection of a strong magnetic field in $z\gtrsim 2.6$ galaxies. Within the assumptions of our simple model, magnetised cold streams emerge as a viable mechanism for seeding a dynamically important galactic magnetic field.