(Proposal ID) S17B-075

(PI) Kakiichi, Koki

(Proposal Title)
The Ionizing Capability of Luminous Galaxies at the End of Cosmic Reionization

(Abstract)
The ionizing output of early star-forming galaxies is key to understanding 
whether they were responsible for cosmic reionization. A major uncertainty is 
the fraction of Lyman continuum photons that can escape into the intergalactic 
medium since this quantity cannot be directly measured beyond a redshift of ~3.
Recent observations suggest rarer luminous galaxies may produce a 
proportionally greater ionizing contribution which, if correct, would 
significantly affect our understanding of the reionization process. To address 
this issue, we propose a spectroscopic survey of 5 < z < 6 galaxies in two 
cosmic volumes whose ionization state can be probed independently via 
absorption line spectra of z~6 QSOs. This will enable us to compare the photo-
ionization rate inferred from both the proximity effect and redshift-dependent 
Lyman alpha forest transmission in the QSO spectra to the output of individual 
galaxies of known redshift, luminosity and position relative to the QSO 
sightline in the same cosmic volume. In this way we can determine 
statistically the contribution of luminous galaxies to maintaining the 
ionized state of intergalactic medium at the end of cosmic reionization.