New constraints on the magnetization of the cosmic web using LOFAR Faraday rotation observations

Journal
Date Issued
2020
Author(s)
O'Sullivan, S. P.
•
Brüggen, M.
•
•
•
Locatelli, N. T.
•
Stuardi, C.
•
•
Vernstrom, T.
•
Heald, G.
•
Horellou, C.
•
Shimwell, T. W.
•
Hardcastle, M. J.
•
Tasse, C.
•
Röttgering, H.
DOI
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.
Volume
495
Issue
3
Start page
2607
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2020MNRAS.495.2607O
Rights
open.access
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