Understand
As a result of our limited data on reionization, the total optical depth for electron scattering, $\tau$, limits precision measurements of cosmological parameters from the Cosmic Microwave Background (CMB).
- It was recently shown that the predicted 21-cm signal of neutral hydrogen contains enough information to reconstruct $\tau$ with sub-percent accuracy, assuming that the neutral gas was much hotter than the CMB throughout the entire epoch of reionization.
- Here we relax this assumption and use the global 21-cm signal alone to extract $\tau$ for realistic X-ray heating scenarios.
- We test our model-independent approach using mock data for a wide range of ionization and heating histories and show that an accurate measurement of the reionization optical depth at a sub-percent level is possible in most of the considered scenarios even when heating is not saturated during the epoch of reionization, assuming that the foregrounds are mitigated.