Contributions of dark matter annihilation within ultracompact minihalos to the 21cm background signal

Understand

In the dark age of the universe, any exotic sources, e.g.

• the dark matter annihilation, which inject the energy into the intergalactic medium (IGM) will left some imprint on the 21cm background signal.
• Recently, one new kind of dark matter structure named ultracompact dark matter minihalo (UCMHs) was proposed.
• Near the inner part UCMHs, the distribution of dark matter particles are steeper than that of the general dark matter halos, $\rho_{\rm UCMHs}(r) \sim r^{-2.25}$, and the formation time of UCMHs is earlier, $z_c \sim 1000$.