New constraints on the magnetization of the cosmic web using LOFAR Faraday rotation observations. Issue 3 (21st May 2020)

• Record Type: Journal Article
• Authors: O'Sullivan, S P; Brüggen, M; Vazza, F; Carretti, E; Locatelli, N T; Stuardi, C; Vacca, V; Vernstrom, T; Heald, G; Horellou, C; Shimwell, T W; Hardcastle, M J; Tasse, C; Röttgering, H
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 495:Issue 3(2020)
• Page Start: 2607
• Page End: 2619
• Publication Date: 2020-05-21
• Subjects: techniques: polarimetric -- galaxies: active -- galaxies: magnetic fields -- large-scale structure of Universe -- radio continuum: galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa1395
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Measuring 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.