On the magnetic fields in voids

TL;DR

This paper investigates the origin and strength of magnetic fields in cosmic voids, proposing that cosmic rays from void galaxies and active galactic nuclei could magnetize these large, empty regions of the universe.

Contribution

It introduces a model estimating magnetic field strength and volume filling factors in voids based on cosmic ray transport from galaxies and AGNs.

Findings

Void magnetic fields can reach at least 10^{-15} G.

Cosmic rays can effectively transport magnetic energy into voids.

Magnetic energy from galaxies and AGNs can explain observed void magnetization.

Abstract

We study the possible magnetization of cosmic voids by void galaxies. Recently, observations revealed isolated starforming galaxies within the voids. Furthermore, a major fraction of a voids volume is expected to be filled with magnetic fields of a minimum strength of about $10^{-15}$ G on Mpc scales. We estimate the transport of magnetic energy by cosmic rays (CR) from the void galaxies into the voids. We assume that CRs and winds are able to leave small isolated void galaxies shortly after they assembled, and then propagate within the voids. For a typical void, we estimate the magnetic field strength and volume filling factor depending on its void galaxy population and possible contributions of strong active galactic nuclei (AGN) which border the voids. We argue that the lower limit on the void magnetic field can be recovered, if a small fraction of the magnetic energy contained in the void galaxies or void bordering AGNs is distributed within the voids.