O'Sullivan, S. P.S. P.O'SullivanBrüggen, M.M.BrüggenVAZZA, FrancoFrancoVAZZACARRETTI, EttoreEttoreCARRETTILocatelli, N. T.N. T.LocatelliStuardi, C.C.StuardiVACCA, VALENTINAVALENTINAVACCAVernstrom, T.T.VernstromHeald, G.G.HealdHorellou, C.C.HorellouShimwell, T. W.T. W.ShimwellHardcastle, M. J.M. J.HardcastleTasse, C.C.TasseRöttgering, H.H.Röttgering2025-02-142025-02-1420200035-8711http://hdl.handle.net/20.500.12386/35944Measuring the properties of extragalactic magnetic fields through the effect of Faraday rotation provides a means to understand the origin and evolution of cosmic magnetism. Here, we use data from the LOFAR Two-Metre Sky Survey (LoTSS) to calculate the Faraday rotation measure (RM) of close pairs of extragalactic radio sources. By considering the RM difference (ΔRM) between physical pairs (e.g. double-lobed radio galaxies) and non-physical pairs (i.e. close projected sources on the sky), we statistically isolate the contribution of extragalactic magnetic fields to ΔRM along the line of sight between non-physical pairs. From our analysis, we find no significant difference between the ΔRM distributions of the physical and non-physical pairs, limiting the excess Faraday rotation contribution to <1.9 rad m-2 (${\sim}95{{\ \rm per\ cent}}$ confidence). We use this limit with a simple model of an inhomogeneous universe to place an upper limit of 4 nG on the cosmological co-moving magnetic field strength on Mpc scales. We also compare the RM data with a more realistic suite of cosmological magnetohydrodynamical simulations that explore different magnetogenesis scenarios. Both magnetization of the large-scale structure by astrophysical processes such as galactic and AGN outflows, and simple primordial scenarios with seed magnetic field strengths <0.5 nG cannot be rejected by the current data; while stronger primordial fields or models with dynamo amplification in filaments are disfavoured.STAMPAenArticle10.1093/mnras/staa13952-s2.0-85091974583https://api.elsevier.com/content/abstract/scopus_id/85091974583https://academic.oup.com/mnras/article/495/3/2607/58415292020MNRAS.495.2607OFIS/05 - ASTRONOMIA E ASTROFISICA