The ultimate frontier of 21cm cosmology

Understand

We present the most detailed computation to date of the 21-cm global signal and fluctuations at $z\gtrsim 500$.

• Our calculations include a highly precise estimate of the Wouthuysen-Field (WF) effect and the first explicit calculation of the impact of free-free processes, the two dominant components of the signal at $z\gtrsim 800$.
• We implement a new high-resolution Ly$\alpha$ radiative transfer calculation, coupled to a state-of-the-art primordial recombination code.
• Using these tools, we find a global signal from 21-cm processes alone of roughly 0.01mK at $z\sim1000$, slightly larger than it would be without the WF effect, but much weaker than previous estimates including this effect.