JWST’s GLIMPSE: A view of the faintest galaxies in the first billion years of cosmic time —

Faint high-redshift galaxies in the early universe constrain the properties of dark matter, the early build-up of stellar mass, and which sources reionized the early universe. The first two years of JWST observations have revealed a wealth of constraints on modestly bright galaxies in the first billion years of cosmic time, but the faintest population has remained under-probed. JWST’s Glimpse is a Cycle 2 large program that pairs up to 39 hour integrations with the natural lensing of the massive foreground cluster Abell S1063. These observations probe a new regime of intrinsically faint galaxies (down to MUV of -10 or observed magnitudes of 34) in the early universe. With seven wide and two medium bands, we find a new class of galaxy candidates within the first 200 Myr of cosmic time that must have formed extremely efficiently. We also constrain the number of very faint galaxies in Cosmic Dawn, the star formation histories of early galaxies, and explore how the faintest galaxies contributed to reionization. In this talk I will highlight our preliminary effort to reveal the population of the faintest early galaxies and their impact on the evolution of the universe.