Redshift evolution of extragalactic rotation measures

TL;DR

This study analyzes the evolution of extragalactic rotation measures of quasars, revealing a steady increase in residual rotation measure dispersion up to redshift 1, with implications for cosmic magnetic fields.

Contribution

It provides the first large-scale analysis of RRM evolution with redshift, carefully accounting for uncertainties and outliers, and highlights the need for higher precision future measurements.

Findings

Residual RRM dispersion increases up to z~1

RRM evolution saturates at higher redshifts

Current data cannot distinguish contributions from different cosmic structures

Abstract

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