Polarized thermal emission from dust in a galaxy at redshift 2.6.

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 ^1,2 , but it is not known how early in the Universe such structures formed ³ . 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 1,000 times that of the Milky Way at redshift 2.6, within 2.5 Gyr of the Big Bang ^4,5 . The polarized emission arises from the alignment of dust grains with the local magnetic field ^6,7 . The median polarization fraction is of the order of 1%, similar to nearby spiral galaxies ⁸ . Our observations support the presence of a 5-kiloparsec-scale ordered magnetic field with a strength of around 500 μG or lower, oriented parallel to the molecular gas disk. This confirms that such structures can be rapidly formed in galaxies, early in cosmic history.
(© 2023. The Author(s).)