Redshift evolution of extragalactic rotation measures

Abstract

We obtained rotation measures of 2642 quasars by cross-identification of the\nmost updated quasar catalog and rotation measure catalog. After discounting the\nforeground Galactic Faraday rotation of the Milky Way, we get the residual\nrotation measure (RRM) of these quasars. We carefully discarded the effects\nfrom measurement and systematical uncertainties of RRMs as well as large RRMs\nfrom outliers, and get marginal evidence for the redshift evolution of real\ndispersion of RRMs which steady increases to 10 rad m$^{-2}$ from $z=0$ to\n$z\\sim1$ and is saturated around the value at higher redshifts. The ionized\nclouds in the form of galaxy, galaxy clusters or cosmological filaments could\nproduce the observed RRM evolutions with different dispersion width. However\ncurrent data sets can not constrain the contributions from galaxy halos and\ncosmic webs. Future RM measurements for a large sample of quasars with high\nprecision are desired to disentangle these different contributions.\n