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arXiv · 1403.6123

The Birth of a Galaxy - III. Propelling reionisation with the faintest galaxies

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

Starlight from galaxies plays a pivotal role throughout the process of cosmic reionisation. We present the statistics of dwarf galaxy properties at z > 7 in haloes with masses up to 10^9 solar masses, 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 ($T_{\rm vir} \ge 10^4$ K) haloes, but can occur in haloes down to masses ~10^6 solar masses, especially in neutral regions. Even though these smallest galaxies only host up to 10^4 solar masses of stars, they provide nearly 30 per cent of the ionising photon budget. We find that the galaxy luminosity function flattens above M_UV ~ -12 with a number density that is unchanged at z < 10. The fraction of ionising radiation escaping into the intergalactic medium is inversely dependent on halo mass, decreasing from 50 to 5 per cent in the mass range $\log M/M_\odot = 7.0-8.5$. Using our galaxy statistics in a semi-analytic reionisation 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 Ly$α$ forest observations at z = 4-6.

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John H. Wise, Vasiliy G. Demchenko, Martin T. Halicek, Michael L. Norman, Matthew J. Turk, Tom Abel, Britton D. Smith. 2014-05-19. The Birth of a Galaxy - III. Propelling reionisation with the faintest galaxies. https://doi.org/10.1093/mnras%2Fstu979

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