A Burst of Reionization in the Dark Ages
Abstract
Primordial overdensities at small scales can be significantly larger than those observed at large scales. As a result, they can collapse much earlier, at redshifts z ∼ 100. In these collapsed halos, stars and black holes can form, where they can then contribute to an early reionization of the universe. If this epoch is temporary, the free electrons will recombine yielding a low level of ionization leading into cosmic dawn. This contributes to the optical depth of the universe, and adds more weakly to low-ℓ polarization signals of ionization compared to later sources. We study the effects of a redshift-localized source of reionization Δτburst in the context of a broad suite of cosmological data to constrain this scenario, finding a preference of approximately ∼ 2−2.5σ for a new contribution. Regardless of Planck reprocessing used (PR3 - SRoll2+plik or PR4 - LoLLiPoP+CamSpec/HiLLiPoP), the results are consistent, favoring a new contribution Δτburst ∼ 0.012 (0.001 < Δτburst < 0.022 at 95\%) and a similar total optical depth τ∼ 0.073. The precise era of reionization is somewhat discrepant depending on the higher-ℓ reprocessing used, with HiLLiPoP favoring z∼ 45, CamSpec z∼ 100 and plik z∼ 165. If such a source is present at 40≲ z≲150, LiteBIRD should be able to detect it, while Simons Observatory should also constrain it.
Related
- hyprfine: simulating the 21-cm signal from the Dark Ages through to the Epoch of Reionization on a GPU
- Unveiling the Dark Ages: A New Pathway Using Tomographical 21 cm Cosmic Microwave Background Cross-correlations
- Wedge-avoidance Fisher Forecasts for Primordial Features from Dark-Ages 21-cm Power Spectrum and Bispectrum
- Stacking HI in the dark: Towards detecting the reionization-epoch 21 cm signal in Lyman-α dark gaps
- Probing Minihalos in the Late Dark Ages through Velocity Acoustic Oscillations in the 21-cm Power Spectrum
BibTeX
@misc{weiner2026burst,
title = {{A Burst of Reionization in the Dark Ages}},
author = {Neal Weiner and Soubhik Kumar and Wenzer Qin and Zilu Zhou and Yacine Ali-Haïmoud and Hector Afonso G. Cruz},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.12552},
eprint = {2610.12552},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.12552},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A Burst of Reionization in the Dark Ages
AU - Neal Weiner
AU - Soubhik Kumar
AU - Wenzer Qin
AU - Zilu Zhou
AU - Yacine Ali-Haïmoud
AU - Hector Afonso G. Cruz
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.12552
UR - https://arxiv.org/abs/2610.12552
AB - Primordial overdensities at small scales can be significantly larger than those observed at large scales. As a result, they can collapse much earlier, at redshifts z ∼ 100. In these collapsed halos, stars and black holes can form, where they can then contribute to an early reionization of the universe. If this epoch is temporary, the free electrons will recombine yielding a low level of ionization leading into cosmic dawn. This contributes to the optical depth of the universe, and adds more weakly to low-ℓ polarization signals of ionization compared to later sources. We study the effects of a redshift-localized source of reionization Δτ_burst in the context of a broad suite of cosmological data to constrain this scenario, finding a preference of approximately ∼ 2−2.5σ for a new contribution. Regardless of Planck reprocessing used (PR3 - SRoll2+plik or PR4 - LoLLiPoP+CamSpec/HiLLiPoP), the results are consistent, favoring a new contribution Δτ_burst ∼ 0.012 (0.001 < Δτ_burst < 0.022 at 95\%) and a similar total optical depth τ∼ 0.073. The precise era of reionization is somewhat discrepant depending on the higher-ℓ reprocessing used, with HiLLiPoP favoring z∼ 45, CamSpec z∼ 100 and plik z∼ 165. If such a source is present at 40≲ z≲150, LiteBIRD should be able to detect it, while Simons Observatory should also constrain it.
ER -