Magnetogenesis and the Cosmic Web: A Joint Challenge for Radio Observations and Numerical Simulations

Franco Vazza,Kamlesh Rajpurohit,Giannandrea Inchingolo,Denis Wittor,Nicola Locatelli,Claudio Gheller,Fabio Finelli,Stefan Hackstein,Matteo Angelinelli,Chiara Stuardi,Stefano Ettori,Daniele Dallacasa,Marcus Brüggen,Gianfranco Brunetti,Daniela Paoletti,Paola Domínguez-Fernández,Serena Banfi,Annalisa Bonafede,Marisa Brienza

doi:10.3390/galaxies9040109

Abstract

The detection of the radio signal from filaments in the cosmic web is crucial to distinguish possible magnetogenesis scenarios. We review the status of the different attempts to detect the cosmic web at radio wavelengths. This is put into the context of the advanced simulations of cosmic magnetism carried out in the last few years by our MAGCOW project. While first attempts of imaging the cosmic web with the MWA and LOFAR have been encouraging and could discard some magnetogenesis models, the complexity behind such observations makes a definitive answer still uncertain. A combination of total intensity and polarimetric data at low radio frequencies that the SKA and LOFAR2.0 will achieve is key to removing the existing uncertainties related to the contribution of many possible sources of signal along deep lines of sight. This will make it possible to isolate the contribution from filaments, and expose its deep physical connection with the origin of extragalactic magnetism.

Highlights

This is put into the context of the advanced simulations of cosmic magnetism carried out in the last few years by our MAGCOW project
Such differences persist in the denser environment of cluster outskirts, where the magnetic field strengths are better approximated by the adiabatic |B| ∝ (ρ/ ρ )2/3 relation
On densities larger than the typical density enclosed by virialised halos, all models struggle to match the magnetisation observed in real clusters and groups

Summary

Introduction

Theoretical and numerical work has shown that the microgauss (μG) magnetic fields inferred from radio observations e.g., [1–4] could be produced by small-scale turbulent dynamo amplification, provided that the magnetic Reynolds number in the intracluster medium (ICM1) is large enough e.g., [5–8]. While all previous results are based on ideal magneto-hydrodynamical (MHD) simulations, kinetic simulations have recently started to explore the more realistic situation of weakly collisional plasmas. They confirmed the action of a dynamo and highlighted the important role of Prandtl number variations on the initial magnetisation value and of kinetic instabilities e.g., [18–20]

Methods

Results

Conclusion