The contribution of the IGM and minihalos to the 21 cm signal of reionization

TL;DR

This study models the 21 cm signal during reionization, showing the IGM dominates over minihalos, which have limited direct detectability but influence the IGM's ionization and flux.

Contribution

It provides a self-consistent simulation of minihalo photoevaporation and compares different thermal states of the IGM to assess their impact on the 21 cm signal.

Findings

IGM signal generally dominates over minihalos.

Minihalo brightness temperature never exceeds 2 mK.

Detection of minihalo signals is likely unfeasible with planned telescopes.

Abstract

We study the statistical properties of the cosmological 21 cm signal from both the intergalactic medium (IGM) and minihalos, using a reionization simulation that includes a self--consistent treatment of minihalo photoevaporation. We consider two models for minihalo formation and three typical thermal states of the IGM -- heating purely by ionization, heating from both ionizing and $\rm Ly\alpha$ photons, and a maximal "strong heating" model. We find that the signal from the IGM is almost always dominant over that from minihalos. In our calculation, the differential brightness temperature, ${\delta}T_b,$ of minihalos is never larger than 2 mK. Although there are indeed some differences in the signals from the minihalos and from the IGM, even with the planned generation of radio telescopes it will be unfeasible to detect them. However, minihalos significantly affect the ionization state of the IGM and the corresponding 21 cm flux.