Volume 501 - 39th International Cosmic Ray Conference (ICRC2025) - Cosmic-Ray Direct & Acceleration
Cosmic Ray Heating in the Early Universe: Joule Heating by Return Currents and its Impact on the Thermal Evolution of the Intergalactic Medium at Redshift around 10
S. Yokoyama* and Y. Ohira
*: corresponding author
Full text: pdf
Pre-published on: September 23, 2025
Published on: December 30, 2025
Abstract
We investigate heating mechanisms of the neutral intergalactic medium (IGM) around galaxies at $z\sim 10$ with a focus on cosmic ray (CR) effects.
Besides conventional X-ray heating and direct CR heating via ionization and Coulomb collisions, we examine CR-driven resistive heating caused by return currents induced by streaming CRs.
We include both Coulomb and charge-neutral collisions in modeling the resistivity and account for their dependence on temperature and ionization degree.
Numerical results show that CR-driven resistive heating can dominate over the other mechanisms, rapidly increasing the IGM temperature to $10^4 \, \mathrm{K}$ near the galaxy and creating a hot region with $T\gtrsim 10^2 \, \mathrm{K}$ extending to $\sim 30 \, \mathrm{kpc}$.
The size and ionization state of this region depend on the star formation rate, suggesting that future $21$-$\mathrm{cm}$ line observations could probe the impact of CRs on the early IGM.
DOI: https://doi.org/10.22323/1.501.0157
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