The galaxies that reionized the Universe
Milan Rai\v{c}evi\'c, Tom Theuns, Cedric Lacey

TL;DR
This study uses the GALFORM model to demonstrate that faint, merger-triggered starburst galaxies could have produced enough ionizing photons to reionize the Universe by redshift 10, mainly from galaxies below current detection limits.
Contribution
It shows that faint, merger-driven starburst galaxies in the GALFORM model can account for cosmic reionization by z=10, highlighting the role of undetected galaxies.
Findings
Faint galaxies dominate ionizing photon production at z=10.
Most ionizing photons come from galaxies below current detection limits.
Merger-triggered starbursts cause significant luminosity dispersion.
Abstract
The Durham GALFORM semi-analytical galaxy formation model has been shown to reproduce the observed rest-frame 1500\AA\ 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. Photo-ionization suppression of star formation in these galaxies is unlikely to affect this conclusion significantly, because the gas that fuels the starbursts has already…
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