A numerical model of resistive generation of intergalactic magnetic field at cosmic dawn

TL;DR

This paper develops a numerical model to simulate the resistive generation of magnetic fields in the intergalactic medium during cosmic dawn, confirming earlier estimates of seed magnetic field strengths.

Contribution

It introduces an approximate numerical implementation of the resistive magnetic seed generation mechanism in a cosmological simulation code.

Findings

Magnetic seed fields between 10^{-18} and 10^{-16} Gauss at redshift z~6.

Results are consistent with magnetic field estimates in voids at z~0.

Supports the viability of resistive processes in early magnetic field generation.

Abstract

Miniati and Bell (2011) proposed a mechanism for the generation of magnetic seeds that is based the finite resistivity of the low temperature IGM in the high redshift universe. In this model, cosmic-ray protons generated by the first generation of galaxies, escape into the intergalactic medium carrying an electric current that induces return currents, $j_t$, and associated electric fields, $\vec E=\eta\vec j_t$ there. Because the resistivity, $\eta$, depends on the IGM temperature, which is highly inhomogeneous due to adiabatic contraction and shocks produced by structure formation, a non-vanishing curl of the electric field exists which sustains the growth of magnetic field. In this contribution we have developed an approximate numerical model for this process by implementing the source terms of the resistive mechanism in the cosmological code CHARM. Our numerical estimates substantiate the earlier analysis in Miniati and Bell (2011) which found magnetic seeds between 10$^{-18}$ and 10$^{-16}$ Gauss throughout cosmic space at redshift z~6, consistent with conservative estimates of magnetic fields in voids at z~0 from recent gamma-ray experiments.