# Limiting Magnetic Fields in the Cosmic Web with Diffuse Radio Emission

## TL;DR

This study constrains the magnetic field strength in the cosmic web by analyzing diffuse radio emission and cross-correlating observational data with MHD simulations, setting upper limits on magnetic fields and primordial magnetic fields.

## Contribution

It introduces a method combining radio survey data with constrained MHD simulations to set new upper limits on cosmic web magnetic fields.

## Key findings

- Upper limit on synchrotron surface brightness in filaments: 0.16 mJy/arcmin^2
- Upper limit on filament magnetic field: 0.03 μG (density-weighted)
- Primordial magnetic field limit: ~1.0 nG

## Abstract

We set limits on the presence of the synchrotron cosmic web through the cross-correlation of the 2.3 GHz S-PASS survey with a model of the local cosmic web derived from constrained magnetohydrodynamic (MHD) simulations. The MHD simulation assumes cosmologically seeded magnetic fields amplified during large-scale structure formation, and a population of relativistic electrons/positrons from proton-proton collisions within the intergalactic medium. We set a model-dependent 3$\sigma$ upper limit on the synchrotron surface brightness of 0.16 mJy arcmin$^{-2}$ at 2.3 GHz in filaments. Extrapolating from magnetic field maps created from the simulation, we infer an upper limit (density-weighted) magnetic field of 0.03 (0.13) $\mu$G in filaments at the current epoch, and a limit on the primordial magnetic field (PMF) of B$_{PMF}$~1.0 nG.