Journal Article

The galaxies that reionized the Universe

Milan Raičević, Tom Theuns and Cedric Lacey

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 410, issue 2, pages 775-787
Published in print January 2011 | ISSN: 0035-8711
Published online December 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17480.x
The galaxies that reionized the Universe

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The Durham galform semi-analytical galaxy formation model has been shown to reproduce the observed rest-frame 1500-Å luminosity function of galaxies well over the whole redshift range z= 5–10. We show that in this model, this galaxy population also emits enough ionizing photons to reionize the Universe by redshift z= 10, assuming a modest escape fraction of 20 per cent. The bulk of the ionizing photons is produced in faint galaxies during starbursts triggered by galaxy mergers. The bursts introduce a dispersion up to ∼5 dex in galaxy-ionizing luminosity at a given halo mass. Almost 90 per cent of the ionizing photons emitted at z= 10 are from galaxies below the current observational detection limit at that redshift. Photoionization suppression of star formation in these galaxies is unlikely to affect this conclusion significantly, because the gas that fuels the starbursts has already cooled out of their host haloes. The galaxies that dominate the ionizing emissivity at z= 10 are faint, with M1500,AB∼−16, have low star formation rates, −1, and reside in haloes of mass M∼109 h−1 M.

Keywords: galaxies: evolution; galaxies: formation; galaxies: high-redshift; intergalactic medium; dark ages, reionization, first stars

Journal Article.  10807 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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