HERA Phase I Limits on the Cosmic 21-cm Signal: Constraints on Astrophysics and Cosmology During the Epoch of Reionization
Creators: name: The HERA Collaboration
name: Abdurashidova, Zara
name: Aguirre, James E.
name: Alexander, Paul
name: Ali, Zaki
name: Balfour, Yanga
name: Barkana, Rennan
name: Beardsley, Adam
name: Bernardi, Gianni
name: Billings, Tashalee
name: Bowman, Judd
name: Bradley, Richard
name: Bull, Phillip
name: Burba, Jacob
name: Carey, Steven
name: Carilli, Christopher
name: Cheng, Carina
name: DeBoer, David
name: Dexter, Matthew
name: Acedo, Eloy de Lera
name: Dillon, Joshua
name: Ely, John
name: Ewall-Wice, Aaron
name: Fagnoni, Nicolas
name: Fialkov, Anastasia
name: Fritz, Randall
name: Furlanetto, Steven
name: Gale-Sides, Kingsley
name: Glendenning, Brian
name: Gorthi, Deepthi
name: Greig, Bradley
name: Grobbelaar, Jasper
name: Halday, Ziyaad
name: Hazelton, Bryna
name: Heimersheim, Stefan
name: Hewitt, Jacqueline
name: Hickish, Jack
name: Jacobs, Daniel
name: Julius, Austin
name: Kern, Nicholas
name: Kerrigan, Joshua
name: Kittiwisit, Piyanat
name: Kohn, Saul
name: Kolopanis, Matthew
name: Lanman, Adam
name: La Plante, Paul
name: Lekalake, Telalo
name: Lewis, David
name: Liu, Adrian
name: Ma, Yin-Zhe
name: MacMahon, David
name: Malan, Lourence
name: Malgas, Cresshim
name: Maree, Matthys
name: Martinot, Zachary
name: Matsetela, Eunice
name: Mesinger, Andrei
name: Mirocha, Jordan
name: Molewa, Mathakane
name: Morales, Miguel
name: Mosiane, Tshegofalang
name: Munoz, Julian
name: Murray, Steven
name: Neben, Abraham
name: Nikolic, Bojan
name: Nunhokee, Chuneeta Devi
name: Parsons, Aaron
name: Patra, Nipanjana
name: Pieterse, Samantha
name: Pober, Jonathan
name: Qin, Yuxiang
name: Razavi-Ghods, N.
name: Reis, Itamar
name: Ringuette, Jon
name: Robnett, James
name: Rosie, Kathryn
name: Santos, Mario
name: Sikder, Sudipta
name: Sims, Peter
name: Smith, Craig
name: Syce, Angelo
name: Thyagarajan, Nithyanandan
name: Williams, Peter
name: Zheng, Haoxuan
Publisher: name: arXiv
Year: 2021
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Recently, the Hydrogen Epoch of Reionization Array (HERA) collaboration has produced the experiment's first upper limits on the power spectrum of 21-cm fluctuations at z~8 and 10. Here, we use several independent theoretical models to infer constraints on the intergalactic medium (IGM) and galaxies during the epoch of reionization (EoR) from these limits. We find that the IGM must have been heated above the adiabatic cooling threshold by z~8, independent of uncertainties about the IGM ionization state and the nature of the radio background. Combining HERA limits with galaxy and EoR observations constrains the spin temperature of the z~8 neutral IGM to 27 K &lt; T_S &lt; 630 K (2.3 K &lt; T_S &lt; 640 K) at 68% (95%) confidence. They therefore also place a lower bound on X-ray heating, a previously unconstrained aspects of early galaxies. For example, if the CMB dominates the z~8 radio background, the new HERA limits imply that the first galaxies produced X-rays more efficiently than local ones (with soft band X-ray luminosities per star formation rate constrained to L_X/SFR = { 10^40.2, 10^41.9 } erg/s/(M_sun/yr) at 68% confidence), consistent with expectations of X-ray binaries in low-metallicity environments. The z~10 limits require even earlier heating if dark-matter interactions (e.g., through millicharges) cool down the hydrogen gas. Using a model in which an extra radio background is produced by galaxies, we rule out (at 95% confidence) the combination of high radio and low X-ray luminosities of L_{r,ν}/SFR &gt; 3.9 x 10^24 W/Hz/(M_sun/yr) and L_X/SFR&lt;10^40 erg/s/(M_sun/yr). The new HERA upper limits neither support nor disfavor a cosmological interpretation of the recent EDGES detection. The analysis framework described here provides a foundation for the interpretation of future HERA results.
description: 40 pages, 19 figures, accepted to ApJ