Polarized thermal emission from dust in a galaxy at redshift 2.6

TL;DR

This study detects polarized dust emission in a high-redshift galaxy, revealing that large-scale magnetic fields can form rapidly within 2.5 billion years after the Big Bang, influencing early galaxy evolution.

Contribution

First detection of polarized dust emission in a galaxy at redshift 2.6, demonstrating early formation of large-scale magnetic fields in the universe.

Findings

Presence of a 5 kpc-scale ordered magnetic field.

Magnetic field strength around 500 microGauss or lower.

Polarization fraction similar to nearby galaxies.

Abstract

Magnetic fields are fundamental to the evolution of galaxies, playing a key role in the astrophysics of the interstellar medium and star formation. Large-scale ordered magnetic fields have been mapped in the Milky Way and nearby galaxies, but it is not known how early in the Universe such structures form. Here we report the detection of linearly polarized thermal emission from dust grains in a strongly lensed, intrinsically luminous galaxy that is forming stars at a rate more than a thousand times that of the Milky Way at redshift 2.6, within 2.5 Gyr of the Big Bang. The polarized emission arises from the alignment of dust grains with the local magnetic field. The median polarization fraction is of order one per cent, similar to nearby spiral galaxies. Our observations support the presence of a 5 kiloparsec-scale ordered magnetic field with a strength of around 500uG or lower, orientated parallel to the molecular gas disk. This confirms that such structures can be rapidly formed in galaxies, early in cosmic history.