The epoch of reionization, when the intergalactic gas went from being neutral and opaque to being very highly ionized, and therefore transparent, is a key period in the evolution of the Universe. Determining the redshift when this occurred and the sources of the photons that ionized the intergalactic gas represents one of the current frontiers in observational cosmology. The enormous recent progress in identifying populations of high-redshift galaxies, particularly the Lyman alpha emitting galaxies, has the potential to answer the question of when this process occurred. This project will develop large, homogeneous galaxy samples with which to determine the properties of the ultra-luminous galaxies at high redshift. An important aspect of this project is to provide research opportunities for graduate and undergraduate students that will engage their interest and encourage their participation in science, train them in observational methods and instruments, direct them in computer processing and reduction techniques for large imaging and spectroscopic data sets, and provide mentoring, with a particular emphasis on encouraging women students.
Observations suggesting a drop in the high-redshift Lyman Alpha Emitter (LAE) fraction beyond a redshift of seven have been interpreted as marking the onset of reionization at this redshift. However, the most luminous LAEs do not appear to show such an evolution and may also exhibit more complex line profiles than lower-luminosity LAEs, suggesting that the most luminous LAEs are protecting themselves from the evolving neutrality of the IGM by generating highly ionized surroundings. As a consequence, the galaxy can be seen directly without scattering from the surrounding intergalactic medium. The aim of the proposed survey is to observe a 120 square degree field to moderate depth using Hyper Suprime-Cam on the Subaru telescope in order to develop a large uniformly-selected sample of very luminous LAEs, as well as a very large sample of more moderate-luminosity LAEs from which we can determine the properties of LAEs from redshift 5 to redshift 7. From these samples, the researchers will be able to determine how LAEs depend on environment and luminosity in this redshift range, as well as estimate the ionizing photon production in the most luminous LAEs and the growth of HII porosity. Determining properties of galaxies near the reionization boundary, and particularly their ionizing photon production, will provide strong constraints on theoretical models of the evolution of the intergalactic gas, the evolution of galaxies, and structure formation at high redshift.
