Lux Ex Tenebris: The Imprint of Annihilating Dark Matter on the Intergalactic Medium during Cosmic Dawn

Abstract

Upcoming measurements of the highly redshifted 21 cm line with next-generation radio telescopes such as the Hydrogen Epoch of Reionization Array (HERA) and Square Kilometer Array will provide the intriguing opportunity to probe dark matter (DM) physics during the Epoch of Reionization, 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 × 512 3 particles in a (100 h −1 Mpc) 3 box with DM annihilation and baryonic cooling physics. We focus on redshift z  ∼ 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 weakly interacting massive particles heavier than m χ ≳ 100 MeV, heating from (GeV) DM particles may leave a significant imprint on the IGM that alters the 21 cm 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.