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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

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 109 M, 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 ∼106 M, especially in neutral regions. Even though these smallest galaxies only host up to 104 M 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 log M/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
Pages (from-to)2560-2579
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Volume442
Issue number3
Early online date26 Jun 2014
DOIs
Publication statusPublished - 11 Aug 2014

Keywords

  • radiative transfer
  • methods: numerical
  • galaxies: dwarf
  • galaxies: formation
  • galaxies: high-redshift
  • dark ages
  • reionization
  • first stars
  • HIGH-REDSHIFT GALAXIES
  • LYMAN-CONTINUUM EMISSION
  • STAR-FORMING GALAXIES
  • ULTRA-DEEP FIELD
  • SIMILAR-TO 8
  • RADIATIVE-TRANSFER SIMULATIONS
  • EXTRAGALACTIC LEGACY SURVEY
  • ACTIVE GALACTIC NUCLEI
  • HUBBLE-SPACE-TELESCOPE
  • BILLION YEARS PROJECT

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