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  • Open Access

Inferring population III star properties from the 21-cm global signal

Sho Ukai1,*, Hayato Shimabukuro1,2,3, Kenji Hasegawa4, and Kiyotomo Ichiki1,5,6

  • 1Graduate School of Science, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi, 464-8602, Japan
  • 2South-Western Institute for Astronomy Research (SWIFAR), Yunnan University, Kunming, Yunnan 650500, People’s Republic of China
  • 3Key Laboratory of Survey Science of Yunnan Province, Yunnan University, Kunming, Yunnan 650500, People’s Republic of China
  • 4Department of Mechanical Engineering, National Institute of Technology, Suzuka College, Shiroko-cho, Suzuka, Mie 510-0294, Japan
  • 5Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
  • 6Institute for Advanced Research, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan

  • *Contact author: ukai.sho.x7@s.mail.nagoya-u.ac.jp
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Phys. Rev. D 114, 063552 – Published 30 September, 2026

DOI: https://doi.org/10.1103/fxst-1k13

Abstract

Investigating the properties of the first stars in the Universe, known as population III (pop III) stars, is essential, yet it remains an open question. One way to explore these stars is by examining their effects on the surrounding gas during the cosmic dawn. In this study, we investigate whether the 21-cm global signal can constrain the typical mass and star formation efficiency of first-generation stars. We perform seminumerical simulations that include the escape fraction of ionizing photons, which depends on stellar and halo masses, as well as the heating structure surrounding a halo that hosts the first star, determined by radiation hydrodynamics simulations. Using a Fisher analysis that includes thermal noise for an integration time of 1000 h, we find that the global signal provides information for constraining these properties if the foreground spectrum can be perfectly removed. However, when the smooth foreground spectrum is modeled using a log-polynomial and inferred from the same data, its spectral variation becomes strongly degenerate with the changes produced by the Pop III parameters, substantially weakening the constraints. These results demonstrate that accurate foreground modeling and removal are essential for extracting information about Pop III properties from the global 21-cm signal.

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Phys. Rev. D 114, 063552– Published 30 September, 2026
  • Received 3 April 2026
  • Accepted 26 August 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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