Evidence for asymmetric reionization histories from a joint analysis of the cosmic microwave background and astrophysical data

Paoletti D. Hazra D.K. Finelli F. Smoot G.F.
15 February 2025 American Physical Society

Physical Review D
2025 #111 Issue 4

We show that by jointly fitting cosmic microwave background (CMB) and astrophysical data - a compilation of UV luminosity data from the Hubble Frontier Field and neutral hydrogen data from distant source - we can infer on the shape of the evolution of the ionized hydrogen fraction with redshift, in addition to constraining the average optical depth τ. For this purpose, we introduce here a novel extended model that includes hydrogen ionization histories which are monotonic with redshift, but allow for an asymmetry, as indicated from our previous works on a free-form reconstruction of reionization. By using our baseline data combination, we obtain τ=0.0542-0.0028+0.0017, consistent with our previous works and tighter than the one inferred by Planck 2018 data because of the combination of CMB with astrophysical data. We find that the symmetric hypothesis within our parametrization is disfavored at 4σ. We test our findings by using alternative likelihoods for CMB polarization at low multipoles, i.e. based on the 2020 reprocessing of Planck high frequency instrument data or on the joint analysis of Wilkinson microwave anisotropy probe and Planck low frequency instrument data, obtaining consistent results that disfavor the symmetric hypothesis of the reionization history at a high statistically significant level. These results will be further tested by more precise astrophysical data such as that from JWST and Euclid deep fields.

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INAF OAS Bologna, Osservatorio di Astrofisica e Scienza Dello Spazio di Bologna, via Gobetti 101, Bologna, I-40129, Italy
The Institute of Mathematical Sciences, CIT Campus, Taramani, Chennai, 600113, India
INFN, Sezione di Bologna, via Irnerio 46, Bologna, 40126, Italy
IAS TT and WF Chao Foundation, IAS, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, 999077, Hong Kong
Homi Bhabha National Institute, Anushaktinagar, Mumbai, 400094, India
Paris Centre for Cosmological Physics, Université de Paris Cité, CNRS, Astroparticule et Cosmologie, Paris, F-75013, France
A, 10 rue Alice Domon et Leonie Duquet, CEDEX 13, Paris, 75205, France
Donostia International Physics Center (DIPC), The Basque Country, Donostia, 20018, Spain
Energetic Cosmos Laboratory, Nazarbayev University, Astana, Kazakhstan
University of California at Berkeley, Physics Department and LBNL, Berkeley, CA, United States

INAF OAS Bologna
The Institute of Mathematical Sciences
INFN
IAS TT and WF Chao Foundation
Homi Bhabha National Institute
Paris Centre for Cosmological Physics
A, 10 rue Alice Domon et Leonie Duquet, CEDEX 13, Paris, 75205, France
Donostia International Physics Center (DIPC)
Energetic Cosmos Laboratory
University of California at Berkeley

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