Lux ex tenebris: The imprint of annihilating dark matter on the intergalactic medium during Cosmic Dawn

TL;DR

This paper investigates how annihilating dark matter particles influence the intergalactic medium during Cosmic Dawn, using hydrodynamic simulations to predict potential observable effects on the 21cm signal.

Contribution

First hydrodynamic simulation study examining the impact of dark matter annihilation on the IGM during Cosmic Dawn, highlighting effects of GeV-scale DM on the 21cm signal.

Findings

DM annihilation affects IGM heating at GeV scales

Structure formation remains unaffected by heavy WIMPs

Low density regions are most sensitive to DM heating

Abstract

Upcoming measurements of the highly redshifted 21cm line with next-generation radio telescopes such as HERA and SKA will provide the intriguing opportunity to probe dark matter (DM) physics during the Epoch of Reionization (EoR), Cosmic Dawn, and the Dark Ages. With HERA already under construction, there is a pressing need to thoroughly understand the impact of DM physics on the intergalactic medium (IGM) during these epochs. We present first results of a hydrodynamic simulation suite with $2 \times 512^3$ particles in a $(100 \ h^{-1} \ \text{Mpc})^3$ box with DM annihilation and baryonic cooling physics. We focus on redshift $z \sim 11$, just before reionization starts in our simulations, and discuss the imprint of DM annihilation on the IGM and on structure formation. We find that whereas structure formation is not affected by thermal WIMPs heavier than $m_\chi \gtrsim 100 \ \text{MeV}$, heating from $\mathcal{O}$(GeV) DM particles may leave a significant imprint on the IGM that alters the 21cm signal. Cold gas in low density regions is particularly susceptible to the effects of DM heating. We note, however, that delayed energy deposition is not currently accounted for in our simulations.