DAWN Cake Talk - William M. Baker

Investigating high-z quiescent galaxies with JWST

Abstract

The discovery of quiescent galaxies within the first 1–2 Gyr of cosmic history has fundamentally reshaped our understanding of early galaxy assembly. Using deep JWST imaging and spectroscopy, I will present a systematic census of over 700 massive quiescent galaxies across 2 < z < 7, revealing that early quenching is both more common and more efficient than predicted by our current models, alongside a detailed investigation into a smaller spectroscopic sample exploring their star-formation histories and AGN activity.

These systems exhibit remarkably mature stellar populations, high stellar masses, compact morphologies, and early formation epochs, implying rapid and intense assembly at z ≳ 6–10 followed by equally rapid shutdown of star formation. I will show that their number densities exceed theoretical expectations as probed by our best cosmological simulations and that simulations are unable to reproduce their stellar mass functions, posing significant challenges to galaxy formation models and their prescriptions for star formation efficiency and feedback at early times.

Moving to less massive systems, I will present results on lower mass quiescent galaxies, showing the two most distant spectroscopically confirmed to-date. Together, these populations suggest that quiescence is not only a late-time phenomenon but instead a fundamental aspect of galaxy evolution operating across mass scales since cosmic dawn.