Comoving IGMF redshift evolution

We use data from the LOFAR Two-Metre Sky Survey: Data Release 2 (LoTSS DR2) to study the dependence of the Faraday rotation measure (RM) on redshift. By focusing on radio sources that are close in terms of their projection on the sky, but physically unrelated ('random pairs'), we measure the RM difference, {Delta}RM, between the two sources.

Thus, we isolate the extragalactic contribution to {Delta}RM from other contributions. We present a statistical analysis of the resulting sample of random pairs and find a median absolute RM difference |{Delta}RM|=(1.79+/-0.09)rad/m^2^, with |{Delta}RM| uncorrelated both with respect to the redshift difference of the pair and the redshift of the nearer source, and a median excess of random pairs over physical pairs of (1.65+/-0.10)rad/m^2^.