Bridging the Gap between Cosmic Dawn and Reionization Favors Models Dominated by Faint Galaxies

Ankita Bera, Sultan Hassan, Aaron Smith, Renyue Cen, Enrico Garaldi, Rahul Kannan, Mark Vogelsberger

Research output: Contribution to journalArticlepeer-review


It has been claimed that traditional models struggle to explain the tentative detection of the 21 cm absorption trough centered at z ∼ 17 measured by the EDGES collaboration. On the other hand, it has been shown that the EDGES results are consistent with an extrapolation of a declining UV luminosity density, following a simple power law of deep Hubble Space Telescope observations of 4 < z < 9 galaxies. We here explore the conditions by which the EDGES detection is consistent with current reionization and post-reionization observations, including the neutral hydrogen fraction at z ∼ 6-8, Thomson-scattering optical depth, and ionizing emissivity at z ∼ 5. By coupling a physically motivated source model derived from radiative transfer hydrodynamic simulations of reionization to a Markov Chain Monte Carlo sampler, we find that it is entirely possible to reconcile existing high-redshift (cosmic dawn) and low-redshift (reionization) constraints. In particular, we find that high contributions from low-mass halos along with high photon escape fractions are required to simultaneously reproduce cosmic dawn and reionization constraints. Our analysis further confirms that low-mass galaxies produce a flatter emissivity evolution, which leads to an earlier onset of reionization with a gradual and longer duration, resulting in a higher optical depth. While the models dominated by faint galaxies successfully reproduce the measured globally averaged quantities over the first one billion years, they underestimate the late redshift-instantaneous measurements in efficiently star-forming and massive systems. We show that our (simple) physically motivated semianalytical prescription produces results that are consistent with the (sophisticated) state-of-the-art THESAN radiation-magnetohydrodynamic simulation of the reionization.

Original languageEnglish (US)
Article number2
JournalAstrophysical Journal
Issue number1
StatePublished - Dec 1 2023

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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