Improved Constraints on the 21 cm EoR Power Spectrum and the X-Ray Heating of the IGM with HERA Phase I Observations
Authors: Abdurashidova The HERA Collaboration: Zara , Adams Tyrone , Aguirre James E. , Alexander Paul , Ali Zaki S. , Baartman Rushelle , Balfour Yanga , Barkana Rennan , Beardsley Adam P. , Bernardi Gianni , Billings Tashalee S. , Bowman Judd D. , Bradley Richard F. , Breitman Daniela , Bull Philip , Burba Jacob , Carey Steve , Carilli Chris L. , Cheng Carina , Choudhuri Samir , DeBoer David R. , de Lera Acedo Eloy , Dexter Matt , Dillon Joshua S. , Ely John , Ewall-Wice Aaron , Fagnoni Nicolas , Fialkov Anastasia , Fritz Randall , Furlanetto Steven R. , Gale-Sides Kingsley , Garsden Hugh , Glendenning Brian , Gorce Adélie , Gorthi Deepthi , Greig Bradley , Grobbelaar Jasper , Halday Ziyaad , Hazelton Bryna J. , Heimersheim Stefan , Hewitt Jacqueline N. , Hickish Jack , Jacobs Daniel C. , Julius Austin , Kern Nicholas S. , Kerrigan Joshua , Kittiwisit Piyanat , Kohn Saul A. , Kolopanis Matthew , Lanman Adam , La Plante Paul , Lewis David , Liu Adrian , Loots Anita , Ma Yin-Zhe , MacMahon David H. E. , Malan Lourence , Malgas Keith , Malgas Cresshim , Maree Matthys , Marero Bradley , Martinot Zachary E. , McBride Lisa , Mesinger Andrei , Mirocha Jordan , Molewa Mathakane , Morales Miguel F. , Mosiane Tshegofalang , Muñoz Julian B. , Murray Steven G. , Nagpal Vighnesh , Neben Abraham R. , Nikolic Bojan , Nunhokee Chuneeta D. , Nuwegeld Hans , Parsons Aaron R. , Pascua Robert , Patra Nipanjana , Pieterse Samantha , Qin Yuxiang , Razavi-Ghods Nima , Robnett James , Rosie Kathryn , Santos Mario G. , Sims Peter , Singh Saurabh , Smith Craig , Swarts Hilton , Tan Jianrong , Thyagarajan Nithyanandan , Wilensky Michael J. , Williams Peter K. G. , van Wyngaarden Pieter , Zheng Haoxuan 
Published: March 2023

Abstract
We report the most sensitive upper limits to date on the 21 cm epoch of reionization power spectrum using 94 nights of observing with Phase I of the Hydrogen Epoch of Reionization Array (HERA). Using similar analysis techniques as in previously reported limits, we find at 95% confidence that Δ2(k = 0.34 h Mpc−1) ≤ 457 mK2 at z = 7.9 and that Δ2(k = 0.36 h Mpc−1) ≤ 3496 mK2 at z = 10.4, an improvement by a factor of 2.1 and 2.6, respectively. These limits are mostly consistent with thermal noise over a wide range of k after our data quality cuts, despite performing a relatively conservative analysis designed to minimize signal loss. Our results are validated with both statistical tests on the data and end-to-end pipeline simulations. We also report updated constraints on the astrophysics of reionization and the cosmic dawn. Using multiple independent modeling and inference techniques previously employed by HERA Collaboration, we find that the intergalactic medium must have been heated above the adiabatic cooling limit at least as early as z = 10.4, ruling out a broad set of so-called “cold reionization” scenarios. If this heating is due to high-mass X-ray binaries during the cosmic dawn, as is generally believed, our result’s 99% credible interval excludes the local relationship between soft X-ray luminosity and star formation and thus requires heating driven by evolved low-metallicity stars.