New constraints on the magnetic field in filaments of the cosmic web

Understand

Strong accretion shocks are expected to illuminate the warm-hot inter-galactic medium encompassed by the filaments of the cosmic web, through synchrotron radio emission.

• Given their high sensitivity, low-frequency large radio facilities may already be able to detect signatures of this extended radio emission from the region in between two close and massive galaxy clusters.
• In this work we exploit the non-detection of such diffuse emission by deep observations of two pairs of relatively close ($\simeq 10$ Mpc) and massive ($M_{500}\geq 10^{14}M_\odot$) galaxy clusters using the LOw-Frequency ARray (LOFAR).
• By combining the results from the two putative inter-cluster filaments, we derive new independent constraints on the median strength of inter-galactic magnetic fields: $B_{\rm 10 Mpc}< 2.5\times 10^2\,\rm nG\,(95\%\, \rm CL)$.