On the role of galaxies and black holes in reionization
Study of the reionization era has now experiencing a surge of new insights, but the long-standing problem of ‘what reionized the universe’ still remains unsolved. Hubble observations have established a now-commonly-held view that the intrinsically faint galaxies are responsible for driving the reionization process. However, high metal emission lines revealed by recent deep spectroscopy of early galaxies suggest harder ionizing radiation from luminous galaxies and possibly active galactic nuclei, which implies possibly an important role of these luminous galaxies in the reionization process. To address this issue, we conducted a pilot Keck/DEIMOS spectroscopic program surveying 5<z<7 galaxies in the foreground of QSOs, where both states of galaxies and the IGM are simultaneously traced by galaxy spectra and QSO absorption line spectroscopy. This enables us to directly determine the impact of the ionizing radiation from early galaxies and AGN on the physical state of the intergalactic gas. We present initial exciting results from this our ongoing program, demonstrating that the spectroscopic galaxy survey in z~6 QSO fields is a promising way to gain new insights into the reionization era before the arrival of JWST and ELT.