Title:

Chasing Cosmic Dawn and Reionization

Abstract:

The newly launched James Webb Space Telescope (JWST) has expanded our cosmic horizon to the first few hundred million years after the Big Bang, enabling us to observe the build up of the first galaxies. These first galaxies fundamentally altered their surroundings by ‘re’-ionizing intergalactic hydrogen. I will describe how this reionization process is still poorly understood, but how identifying when reionization began and which population of galaxies dominated the process is key to constraining poorly understood astrophysics of galaxy formation (e.g. massive star formation and feedback processes). Excitingly, an excess of luminous galaxy candidates just 500 million years after the Big Bang has been discovered in early JWST data, which exceeds theoretical predictions. I will discuss how the new JWST observations test theoretical models and possible solutions. I will present efforts to constrain the timeline of reionization, which favour a late and rapid end to reionization. I will discuss how JWST observations of Lyman alpha emission at z>8 challenge these results and discuss the implications for our understanding of early star formation.