PhD defense by Ilias Goovaerts

PhD defense by Ilias Goovaerts : “The sources of cosmic reionisation : Evaluating the properties and contribution of faint star-forming galaxies”. It will take place Monday the 16th of September in the amphitheatre at the LAM. The defence will be in English.

Below is the list of jury members:
President: Veronique Buat
Reporter: Françoise Combes
Reporter: Jarle Brinchmann
Examinater: Laura Pentericci
Examinater: Pascal Oesch
Invited: Denis Burgarella
Invited: Nicolas Laporte
Supervisor: Roser Pello

Abstract:
Cosmic reionisation is the last phase transition undergone by the Universe, finishing around z~6. The main contributors to this process are still debated, however evidence has pointed to faint, star-forming galaxies as the main actors. This thesis seeks to characterise and assess the contribution to reionisation of these faint, star-forming galaxies through the use of VLT/MUSE, HST and JWST data, as well as gravitational lensing. For this purpose, the work assembles the largest sample of lensed Lyman-alpha emitters: faint galaxies identified by the Lyman-α emission line (LAEs), and UV-selected galaxies to date (at redshifts between 2.9 and 6.7).
I explore the properties of these galaxies and the relationship of Lyman-α emission to the host galaxy. I also constrain the timeline of reionisation using the fraction of galaxies detected as LAEs, and assess the contribution of this specific population to the reionisation process.
The results support previous findings of LAEs as highly star-forming, dust-poor, young galaxies and particularly stress the anti-correlation between the strength of Lyman-α emission and the UV brightness of the host galaxy. Interesting results are found when looking at the Lyman-α emitting fraction, pointing to UV-bright galaxies ionising bubbles around themselves during the epoch of reionisation and therefore allowing Lyman-α photons to escape.
Finally I find that the LAE population could have provided all the photons necessary for reionisation at z=6 using well-motivated assumptions about the ionising photon efficiency and the escape of ionising photons from these galaxies.