New insights into early galaxy formation with JWST and ALMA

by Dr Joris Wistok (NBI/DAWN, UCPH)

Friday 21 Nov 2025, 10:30 → 12:30 Europe/Stockholm

FC61 (AlbaNova Main Building)

Cosmic reionization began when ultraviolet (UV) radiation produced in the first galaxies began illuminating the cold, neutral gas that filled the primordial Universe. Recent JWST observations have shown that surprisingly UV-bright galaxies were in place beyond redshift z = 14, when the Universe was less than 300 Myr old, sparking a debate on the nature of these early systems. I will present spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES) of a galaxy at redshift z = 13.0 that reveals a singular, bright emission line unambiguously identified as Lyman-α (Lyα), the principal hydrogen transition. Together with an extremely blue UV continuum, the unexpected Lyα emission indicates that the galaxy is a prolific producer and leaker of ionising photons, suggesting that massive, hot stars or an active galactic nucleus have commenced reionization early on. I will further present new observations from the Atacama Large Millimeter/submillimeter Array (ALMA), which have begun to provide vital insights on the gas, metal and dust content of z > 10 galaxies. Comparing the accurate ALMA redshifts to those measured purely from the Lyα break, even spectroscopically, we find damped Lyα absorption can cause systematic overestimates of up to Δz ~ 0.5, suggesting the presence of large neutral gas reservoirs. Several detections of bright [O III] 88 μm emission agree well with local SFR scaling relations, indicating early galaxies rapidly enrich in oxygen (>10% solar) within a few hundred million years after the Big Bang.