The ultimate frontier of 21cm cosmology
Patrick C. Breysse, Yacine Ali-Ha\"imoud, Christopher M. Hirata

TL;DR
This paper provides the most detailed calculations of the 21-cm global signal and fluctuations at very high redshifts, incorporating new effects like free-free processes and advanced radiative transfer, revealing the limits of observability.
Contribution
It introduces a highly precise computation of the 21-cm signal at z>500, including the first explicit impact of free-free processes and advanced Lyα radiative transfer modeling.
Findings
Global 21-cm signal is about 0.01 mK at z~1000, weaker than previous estimates.
Free-free absorption dominates the high-redshift signal, creating a 1-2 mK background.
Fluctuations are too faint and suppressed at high redshift for future detection.
Abstract
We present the most detailed computation to date of the 21-cm global signal and fluctuations at . 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 . We implement a new high-resolution Ly 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 , slightly larger than it would be without the WF effect, but much weaker than previous estimates including this effect. We also find that this signal is swamped by a smooth mK signal due to free-free absorption at high redshift by the partially ionized gas along the line of sight. In addition, we estimate the…
Peer Reviews
No public reviews on file for this paper yet. If you reviewed it on a platform where reviews are public (OpenReview, ICLR, NeurIPS, ICML), you can paste yours below so the community can read it here.
Videos
No videos yet. Explain this paper in a talk, walkthrough, or lecture? Add one.
