Colloquium on Oct. 27, 2022

Probing the first galaxies and cosmic reionization with the James Webb Space Telescope

Speaker: Hakim Atek (IAP)

Venue: Video Conference

Time: 16:00 PM, Thursday, Oct. 27, 2022

Abstract:

The role of dwarf galaxies in the star formation history of the universe has long been overlooked, primarily because of observational challenges and the predominance of bright, photometrically-selected galaxy samples. For instance, the luminosity function  (which indicates the prevalence of galaxies as a function of their luminosity) at high redshift indicates that dwarf galaxies are the dominant population and are therefore the best targets to understand galaxy formation and evolution across cosmic times. In this presentation, I will show how the combination of strong gravitational lensing offered by massive galaxy clusters can help us uncover the smallest structures to form at the earliest epochs. I will present a road map for estimating the contribution of galaxies to cosmic reionization, which marks a global change in the state of the baryonic matter in the Universe. We are now on the verge of probing the extreme faint-end of the luminosity function (galaxies a thousand times fainter than the Milky Way) where we expect the number density of dwarf galaxies to drop due to inefficient star formation.  I will discuss some fundamental implications of this potential turnover regarding the feedback processes that regulate star formation in early galaxies. Finally I will present our discovery of z>10 galaxy candidates with JWST in the MASCS0723 lensing field, including a z~16 candidate, and the implication of their number density on theoretical models of galaxy formation. I will also discuss the stellar population properties of these candidates inferred from SED fitting, including extremely blue UV slopes and young ages. These results highlight the potential of forthcoming deep JWST observations, with the help in particular of strong lensing, such the UNCOVER program.