Turbulent Transport of Galactic Magnetic Fields into Cosmic Voids: Insights from IllustrisTNG

Abstract

Astrophysical processes associated with galaxies may contribute to the magnetization of cosmic voids. We investigate the diffusion of galactic magnetic fields in an expanding universe in the presence of turbulent magnetic diffusivity. To estimate the turbulent magnetic diffusivity, we analyze the TNG50-1 data set of the IllustrisTNG simulation and derive its redshift dependence from the characteristic turbulent velocity and turbulent scale of the intergalactic medium. Using the resulting diffusivity, we find a present-day magnetic screening length of $\sim 7\,{\rm Mpc}$, roughly twenty times larger than previous estimates based on a constant turbulent diffusivity due to the larger turbulent scale obtained in our analysis. This scale corresponds to a significant fraction of the characteristic size of cosmic voids and suggests that galactic magnetic fields can play a more important role in void magnetization than previously estimated.