Most of the photons that reionized the Universe came from dwarf galaxies

Hakim Atek (), Ivo Labbé, Lukas J. Furtak, Iryna Chemerynska, Seiji Fujimoto, David J. Setton, Tim B. Miller, Pascal Oesch, Rachel Bezanson, Sedona H. Price, Pratika Dayal, Adi Zitrin, Vasily Kokorev, John R. Weaver, Gabriel Brammer, Pieter van Dokkum, Christina C. Williams, Sam E. Cutler, Robert Feldmann, Yoshinobu Fudamoto, Jenny E. Greene, Joel Leja, Michael V. Maseda, Adam Muzzin, Richard Pan, Casey Papovich, Erica J. Nelson, Themiya Nanayakkara, Daniel P. Stark, Mauro Stefanon, Katherine A. Suess, Bingjie Wang and Katherine E. Whitaker
Additional contact information
Hakim Atek: Sorbonne Université
Ivo Labbé: Swinburne University of Technology
Lukas J. Furtak: Ben-Gurion University of the Negev
Iryna Chemerynska: Sorbonne Université
Seiji Fujimoto: The University of Texas at Austin
David J. Setton: University of Pittsburgh
Tim B. Miller: Northwestern University
Pascal Oesch: University of Geneva
Rachel Bezanson: University of Pittsburgh
Sedona H. Price: University of Pittsburgh
Pratika Dayal: University of Groningen
Adi Zitrin: Swinburne University of Technology
Vasily Kokorev: University of Groningen
John R. Weaver: University of Massachusetts
Gabriel Brammer: University of Copenhagen
Pieter van Dokkum: Yale University
Christina C. Williams: NSF’s National Optical-Infrared Astronomy Research Laboratory
Sam E. Cutler: University of Massachusetts
Robert Feldmann: University of Zurich
Yoshinobu Fudamoto: Waseda University
Jenny E. Greene: Princeton University
Joel Leja: The Pennsylvania State University
Michael V. Maseda: University of Wisconsin
Adam Muzzin: York University
Richard Pan: Tufts University
Casey Papovich: Texas A&M University
Erica J. Nelson: University of Colorado
Themiya Nanayakkara: Swinburne University of Technology
Daniel P. Stark: University of Arizona
Mauro Stefanon: Universitat de València
Katherine A. Suess: University of California
Bingjie Wang: The Pennsylvania State University
Katherine E. Whitaker: University of Copenhagen

Nature, 2024, vol. 626, issue 8001, 975-978

Abstract: Abstract The identification of sources driving cosmic reionization, a major phase transition from neutral hydrogen to ionized plasma around 600–800 Myr after the Big Bang1–3, has been a matter of debate4. Some models suggest that high ionizing emissivity and escape fractions (fesc) from quasars support their role in driving cosmic reionization5,6. Others propose that the high fesc values from bright galaxies generate sufficient ionizing radiation to drive this process7. Finally, a few studies suggest that the number density of faint galaxies, when combined with a stellar-mass-dependent model of ionizing efficiency and fesc, can effectively dominate cosmic reionization8,9. However, so far, comprehensive spectroscopic studies of low-mass galaxies have not been done because of their extreme faintness. Here we report an analysis of eight ultra-faint galaxies (in a very small field) during the epoch of reionization with absolute magnitudes between MUV ≈ −17 mag and −15 mag (down to 0.005L⋆ (refs. 10,11)). We find that faint galaxies during the first thousand million years of the Universe produce ionizing photons with log[ξion (Hz erg−1)] = 25.80 ± 0.14, a factor of 4 higher than commonly assumed values12. If this field is representative of the large-scale distribution of faint galaxies, the rate of ionizing photons exceeds that needed for reionization, even for escape fractions of the order of 5%.

Date: 2024
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DOI: 10.1038/s41586-024-07043-6

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