Understanding cosmic reionization: The production and escape of ionizing photons in high-redshift galaxies with VANDELS and JWST

by Dr Ryan Begley (University of Edinburgh)

Friday 4 Apr 2025, 10:30 → 12:30 Europe/Stockholm

FC61 (AlbaNova Main Building)

The Epoch of Reionization (EOR) marks a pivotal moment in the Universe’s history when the first galaxies ionized the intergalactic medium, fundamentally transforming the state of the Universe. Despite significant progress in understanding this era, key uncertainties remain, particularly concerning the ionizing properties of young star-forming galaxies (SFGs) that drive this process.
In this talk, I will focus on two critical aspects of reionization: the escape fraction of ionizing (Lyman continuum, LyC) photons, and the ionizing photon production efficiency of high-redshift SFGs. Using the VANDELS survey, I will explore the relationship between LyC escape and other galaxy properties such as Lyα escape, UV luminosity, and stellar mass. These insights offer vital clues about the physical processes shaping the ionization of the early Universe.
Additionally, I will present recent results from JWST that provide key insights into the evolution of ionizing photon production across cosmic time, focusing on the role of SFGs in driving reionization. A strong redshift evolution is observed in the strength of [OIII] + Hβ emission, with equivalent widths increasing by a factor of ~2x from z ∼ 3.5 to z > 7. This increase highlights the bursty star formation histories of high-redshift galaxies. I will also examine correlations between emission line strength, stellar mass, and UV luminosity, shedding light on the diverse star formation processes in the early Universe.
Lastly, I will highlight some exciting recent and ongoing work using EXCELS, a deep JWST/NIRSpec survey enabling detailed investigations into the physical properties across cosmic time of star-forming and quiescent galaxies alike.