Radio Observations as a Probe of Cosmic Web Magnetism

The Universe's magnetogenesis can be investigated with radio observations of cosmic filaments, where the information on the initial magnetic field seeds is expected to be preserved in time. In this work, we update the comparison between recent observational results in filaments with the predictions from recent cosmological simulations to check whether one of them is favoured. The radio probes we use are the rotation measure (RM) of filaments as a function of the redshift ($z$), stacking of synchrotron emission from filaments, and the RM radial profile away from galaxy groups. The first two probes favour the presence of a dominant primordial magnetic field component and disfavour a sole astrophysical scenario, the third probe does not yet give an unambiguous outcome. We also estimate the average field strength in filaments. Independently of the scenario and the shape of the astrophysical component RM, it is in the range 10--60 nG at $z=0$, while, when restricted to the model that gives the best match to the simulations, it gives $43\pm 7$ nG, with an astrophysical component RM rapidly decreasing with the redshift.