Institute for Advanced Study / Princeton University Joint Astrophysics Colloquium

The James Webb Space Telescope (JWST) is finding earlier and brighter sources than expected. In this talk I will explore how these new observations fit (or don’t) within our cosmological and galaxy-formation models. First, I will discuss the unexpectedly high abundance of galaxies in the first few hundred million years of cosmic history (redshift z>9), and how to use cosmological clustering measurements to distinguish between scenarios. Then, I will present the first empirical measurement of how star-formation variability, or burstiness, depends on galaxy mass, a key ingredient for explaining this overabundance. Finally, I will examine emerging tensions between JWST measurements of cosmic reionization and probes such as the CMB and the Lyman-alpha forest, and what they imply for the recent dark energy results from DESI.