Takahiro Morishita (STScI) -- Shedding Light on the Epoch of Reionization with Future Space Telescopes

Recent high-sensitivity observations from space have provided us a glimpse of galaxies and quasars in the Epoch of Reionization (EoR). These populations are believed to play several important roles, e.g., by contributing to reionization and being building blocks of today’s massive galaxies. In this talk, I will start by introducing our latest project, SuperBoRG, which compiled all archival data taken through the HST’s pure-parallel imaging programs in the past decade. From this ideal dataset, we identified ~50 luminous source candidates at 7<z<12 by the photometric dropout technique, including three point sources. The main focus here is on those point sources, which were previously overlooked as foreground interlopers despite the possibility of them being extreme starburst galaxies or low-luminosity quasars instead. I will present our careful photometric analyses in combination with deep spectra taken with Keck/MOSFIRE, to look into their physical properties. I will highlight the critical roles to be carried out by the Euclid satellite and the Nancy Grace Roman Space Telescope in constraining the number densities of such extreme populations. Lastly, I will present an independent approach to early populations through the analyses of “fossil records” in massive quenched galaxies at z~2. By exploiting deep grism datasets taken in multiple HST programs, our new analyses revealed that a significant amount of their mass has already formed by z~6. Our upcoming observations of early quenched populations with the James Webb Space Telescope will shed light on their evolutionary connection to luminous sources in the EoR and aid the direct exploration by Euclid and Roman.