Particle energy cascade in the Intergalactic Medium

Abstract

We study the development of high energy (E_in < 1TeV) cascades produced by a primary electron of energy E_in injected into the intergalactic medium (IGM). To this aim we have developed the new code MEDEA (Monte Carlo Energy DEposition Analysis) which includes Bremsstrahlung and Inverse Compton (IC) processes, along with H/He collisional ionizations and excitations, and electron-electron collisions. The cascade energy partition into heating, excitations and ionizations depends primarily on the IGM ionized fraction, x_e, but also on redshift, z, due to IC on CMB photons. While Bremsstrahlung is unimportant under most conditions, IC becomes largely dominant at energies E_in > 1MeV. The main effect of IC at injection energies E_in < 100MeV is a significant boost of the fraction of energy converted into low energy photons (hν< 10.2eV) which do not further interact with the IGM. For energies E_in > 1GeV CMB photons are preferentially upscattered within the X-ray spectrum ($hν> 10^4eV) and can free stream to the observer. Complete tables of the fractional energy depositions as a function of redshift, E_in and ionized fraction are given. Our results can be used in many astrophysical contexts, with an obvious application related to the study of decaying/annihilating Dark Matter (DM) candidates in the high-z Universe.

16 pages, 6 figures, 21 tables

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• The Darkest Hour Before Dawn: Contributions to Cosmic Reionization from Dark Matter Annihilation and Decay
• Energy Injection And Absorption In The Cosmic Dark Ages
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• The Evolution of 21-cm Structure (EOS): public, large-scale simulations of Cosmic Dawn and Reionization
• Systematic Uncertainties In Constraining Dark Matter Annihilation From The Cosmic Microwave Background
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• The Dark Ages of the Universe and Hydrogen Reionization
• Perturbed Recombination from Dark Matter Annihilation
• Dissecting the Compton scattering kernel I: Isotropic media
• Comparison of numerical methods for computing the repeated Compton scattering of photons in isotropic media
• The Effects of Dark Matter Annihilation on Cosmic Reionization
• Sensitivity toward dark matter annihilation imprints on 21-cm signal with SKA-Low: A convolutional neural network approach
• Energy dissipation of energetic electrons in the inhomogeneous intergalactic medium during the epoch of reionization