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28 March 2024 |
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New constraints on the magnetization of the cosmic web using LOFAR Faraday rotation observations | S. P. O'Sullivan
; M. Brüggen
; F. Vazza
; E. Carretti
; N. Locatelli
; C. Stuardi
; V. Vacca
; T. Vernstrom
; G. Heald
; C. Horellou
; T. W. Shimwell
; M. J. Hardcastle
; C. Tasse
; H. Röttgering
; | Date: |
17 Feb 2020 | 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 ($Delta$RM) 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 the total RM variance along the line of sight.
We find a difference in the rms of $Delta$RM between non-physical and physical
pairs of 0.4$pm$0.3 rad/m$^2$, and a difference in the corresponding median
|$Delta$RM| values of 0.3$pm$0.4 rad/m$^2$. This enables us to place an upper
limit on the co-moving cosmological magnetic field strength of $B < 2.5$ nG on
Mpc scales. This limit is obtained by exploring a wide range of input magnetic
field strengths in a model of cosmic over-densities that realistically reflects
the observed matter inhomogeneities on large scales. We also compare the LOFAR
RM data with a suite of cosmological MHD 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 field strengths of $Blesssim0.5$ nG cannot be
rejected by the current data, while stronger primordial fields or models with
dynamo amplification in filaments are disfavoured. In general, LOFAR polarized
sources are typically located in regions of the Universe with low RM variance,
making them excellent probes of the weak magnetization of cosmic filaments and
voids far from galaxy cluster environments. | Source: | arXiv, 2002.6924 | Services: | Forum | Review | PDF | Favorites |
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