The birth of a galaxy - III. Propelling reionization with the faintest galaxies

John H. Wise, Vasiliy G. Demchenko, Martin T. Halicek, Michael L. Norman, Matthew J. Turk, Tom Abel, Britton D. Smith

Research output: Contribution to journalArticlepeer-review


Starlight from galaxies plays a pivotal role throughout the process of cosmic reionization. We present the statistics of dwarf galaxy properties at z > 7 in haloes with masses up to 109M⊙, using a cosmological radiation hydrodynamics simulation that follows their buildup starting with their Population III progenitors. We find that metal-enriched star formation is not restricted to atomic cooling (Tvir ≥ 104 K) haloes, but can occur in haloes down to masses ∼106M⊙, especially in neutral regions. Even though these smallest galaxies only host up to 104M⊙ of stars, they provide nearly 30 per cent of the ionizing photon budget. We find that the galaxy luminosity function flattens above MUV ∼ -12 with a number density that is unchanged at z ≤ 10. The fraction of ionizing radiation escaping into the intergalactic medium is inversely dependent on halo mass, decreasing from 50 to 5 per cent in the mass range logM/M⊙ = 7.0-8.5. Using our galaxy statistics in a semi-analytic reionization model, we find a Thomson scattering optical depth consistent with the latest Planck results, while still being consistent with the UV emissivity constraints provided by Lyα forest observations at z = 4-6.

Original languageEnglish (US)
Pages (from-to)2560-2579
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Aug 2014
Externally publishedYes


  • dark ages, reionization, first stars
  • galaxies: dwarf
  • galaxies: formation
  • galaxies: high-redshift
  • methods: numerical
  • radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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