  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.
