11:00 AM – 321 Allen Hall and Zoom

Cosmological puzzles from JWST observations

The launch of the James Webb Space Telescope (JWST) has ignited a revolution in our understanding of the early universe. Its exquisite infrared capabilities have allowed observers to find galaxies at higher redshifts than ever before, and to measure their stellar properties. I will describe how, intriguingly, observations in these different arenas appear to be in tension with our models. First, I will discuss the higher-than-expected abundance of z>10 galaxies in JWST, focusing on how clustering measurements can break degeneracies in our models and inform the pathway to form the first galaxies. Then I will show how recent determinations of the ionizing properties of the first galaxies imply an earlier reionization than observed by Planck, showing a tension in our models. If time allows, I will discuss the ultra-massive galaxy candidates argued to be “universe breakers”, and how HST observations at the same redshifts rule out a cosmological departure from LCDM big enough to explain their abundances.