Abstract
An unprecedented array of new observational capabilities are starting to yield key constraints on models of the epoch of first light in the Universe. In this Letter we discuss the implications of the UV radiation background at cosmic dawn inferred by recent JWST observations for radio experiments aimed at detecting the redshifted 21 cm hyperfine transition of diffuse neutral hydrogen. Under the basic assumption that the 21 cm signal is activated by the Lyα photon field produced by metal-poor stellar systems, we show that a detection at the low frequencies of the EDGES and SARAS3 experiments may be expected from a simple extrapolation of the declining UV luminosity density inferred at z ≲ 14 from JWST early galaxy data. Accounting for an early radiation excess above the cosmic microwave background suggests a shallower or flat evolution to simultaneously reproduce low- and high-z current UV luminosity density constraints, which cannot be entirely ruled out, given the large uncertainties from cosmic variance and the faint-end slope of the galaxy luminosity function at cosmic dawn. Our findings raise the intriguing possibility that a high star formation efficiency at early times may trigger the onset of intense Lyα emission at redshift z ≲ 20 and produce a cosmic 21 cm absorption signal 200 Myr after the Big Bang.
| Original language | English (US) |
|---|---|
| Article number | L3 |
| Journal | Astrophysical Journal Letters |
| Volume | 958 |
| Issue number | 1 |
| DOIs | |
| State | Published - Nov 1 2023 |
Funding
The authors acknowledge the anonymous referee for the constructive feedback and suggestions that greatly improved the paper, and thank Adam Lidz, Martin Rey, Ingyin Zaw, Andrea Macci\u00F2, Anthony Pullen, and Patrick Breysse for helpful discussions. S.H. acknowledges support for program number HST-HF2-51507 provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, incorporated, under NASA contract NAS5-26555. C.C.L. acknowledges support from a Dennis Sciama fellowship funded by the University of Portsmouth for the Institute of Cosmology and Gravitation. P.M. acknowledges support from NASA TCAN grant 80NSSC21K0271 and the hospitality of New York University Abu Dhabi during the completion of this work. This research was supported in part by the National Science Foundation under grant No. NSF PHY-1748958. Part of this work was completed during the KITP GALEVO23 workshop for data-driven astronomy. This material is based upon work supported by Tamkeen under the NYU Abu Dhabi Research Institute grant CASS.
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science