Understanding cosmic reionization: the production and escape of Lyman-continuum photons in high-redshift galaxies unveiled with VANDELS and JWST

The quest to gain a full understanding of the Epoch of Reionization (EOR) is hampered by our incomplete knowledge of the ionizing properties of the young star-forming galaxies (SFGs) that drive this phase transition of the Universe. A key limitation is the uncertainty in the fraction of hydrogen ionizing (Lyman continuum) photons that escape galaxies (fesc,LyC) into the intergalactic medium (IGM). In this talk, I will discuss recent measurements of fesc,LyC wielding ultra-deep spectroscopy from the VANDELS survey, and examine its connection with other key galaxy properties such as the escape fraction of Ly𝛼 photons, UV luminosity and stellar mass. Another crucial component required in piecing together the timeline of reionization is the ionizing photon production rate of high-redshift galaxies. Complimentary to constraints on LyC escape, I therefore combined VANDELS with the latest data from JWST to explore the redshift evolution of the average ionizing photon production rate using the [O iii]+H 𝛽 nebular emission of galaxies over the redshift range 2 ≤ 𝑧 ≤ 8.