The nature of dark matter from the global high redshift HI 21 cm signal

TL;DR

This paper investigates how dark matter annihilation impacts the global 21 cm signal during the Dark Ages and Cosmic Reionization, suggesting that future radio observations could reveal dark matter properties through IGM heating signatures.

Contribution

It models the effects of specific dark matter candidates on the 21 cm signal, incorporating structure formation and astrophysical sources, providing new predictions for observational signatures.

Findings

Dark matter annihilation can significantly suppress the 21 cm absorption feature.

Different dark matter candidates produce distinct heating signatures in the 21 cm signal.

Future radio telescopes could detect these signatures, constraining dark matter properties.

Abstract

We study the imprint of dark matter (DM) annihilation on the global 21 cm signal from the Dark Ages to Cosmic Reionization. Motivated by recent observations, we focus on three DM candidates: (i) a 10 GeV Bino-like neutralino (ii) a 200 GeV Wino and (iii) a 1 TeV heavier particle annihilating into leptons. For each DM candidate we assume two values for the thermally averaged annihilation cross section \sigma v, the standard thermal value \sigma v_th = 3 x 10^-26 cm^3 s^-1 and the maximum value allowed by WMAP7 data, \sigma v_max. We include the enhancement of DM annihilations due to collapsed structures, detailed estimates of energy deposition into the intergalactic medium (IGM), as well realistic prescriptions for astrophysical sources of UV and X-ray radiation. In these models, the additional heat input from DM annihilation suppresses the mean 21cm brightness temperature offset by \delta Tb ~ few-100 mK. In particular, the very deep \delta Tb ~ -150 mK absorption feature at ~20 < z < 25 predicted by popular models of the first galaxies is considerably reduced or totally erased by some of the considered DM candidates. Such an enhancement in IGM heating could come from either DM annihilations or a stronger-than-expected astrophysical component (i.e. abundant early X-ray sources). However, we find that the two signatures are not degenerate, since the DM heating is dominated by halos several orders of magnitude smaller than those hosting galaxies, whose fractional abundance evolves more slowly resulting in a smaller gradient: d \delta Tb/d \nu < 4 mK/MHz in the range \nu ~60-80 MHz. The detection of such signals by future radio telescopes would be clear evidence of DM energy injection at high-redshifts.