Polarized accretion shocks from the cosmic web

TL;DR

This paper provides the first observational evidence of polarized synchrotron emission from the cosmic web's accretion shocks, confirming theoretical predictions about magnetic field organization in large-scale structures.

Contribution

It presents the detection of polarized radio emission from cosmic web filaments and cluster peripheries, supported by cosmological simulations, demonstrating shock-accelerated cosmic rays and magnetic field alignment.

Findings

Detected polarization fractions >= 20% in cosmic web regions

Confirmed shock acceleration as the origin of observed radio emission

Supported findings with cosmological simulation comparisons

Abstract

On the largest scales, galaxies are pulled together by gravity to form clusters, which are connected by filaments making a web-like pattern. Radio emission is predicted from this cosmic web, which should originate from the strong accretion shocks around the cosmic structures. We present the first observational evidence that Fermi-type acceleration from strong shocks surrounding the filaments of the cosmic web, as well as in peripherals of low-mass clusters, is at work in the Universe. Using all-sky radio maps and stacking on clusters and filaments, we have detected the polarization signature of the synchrotron emission with polarization fractions >= 20%, which is best explained by the organization of local magnetic fields by strong shock waves both at the cluster peripheries and between clusters. Our interpretation is well supported by a detailed comparison with state-of-the-art cosmological simulations.