Faraday Rotation Measure due to the Intergalactic Magnetic Field

TL;DR

This paper uses cosmological simulations to estimate the Faraday rotation measure caused by the intergalactic magnetic field in galaxy filaments, predicting observable effects that can inform our understanding of cosmic magnetism.

Contribution

It introduces a model for the intergalactic magnetic field based on turbulence dynamo, providing detailed predictions for the Faraday rotation measure in large-scale structures.

Findings

RM in filaments is about 1 rad/m^2.

RM distribution follows a log-normal pattern.

RM power spectrum peaks at ~1 h^{-1} Mpc.

Abstract

Studying the nature and origin of the intergalactic magnetic field (IGMF) is an outstanding problem of cosmology. Measuring Faraday rotation would be a promising method to explore the IGMF in the large-scale structure (LSS) of the universe. We investigated the Faraday rotation measure (RM) due to the IGMF in filaments of galaxies using simulations for cosmological structure formation. We employed a model IGMF based on turbulence dynamo in the LSS of the universe; it has an average strength of $< B > \sim 10$ nG and a coherence length of several $\times\ 100\ h^{-1}$ kpc in filaments. With the coherence length smaller than path length, the inducement of RM would be a random walk process, and we found that the resultant RM is dominantly contributed by the density peak along line of sight. The rms of RM through filaments at the present universe was predicted to be $\sim 1\ {\rm rad\ m^{-2}}$. In addition, we predicted that the probability distribution function of $|{\rm RM}|$ through filaments follows the log-normal distribution, and the power spectrum of RM in the local universe peaks at a scale of $\sim 1\ h^{-1}$ Mpc. Our prediction of RM could be tested with future instruments.