Seminar LAM: Mengyuan Xiao “Bigger, Faster, Earlier: The Rise of Massive Galaxies in the Early Universe”

Over the past three years, JWST has dramatically reshaped our view of how the most massive galaxies emerged in the early Universe. Its deep imaging and spectroscopy have revealed that galaxies assembled their stellar mass far more efficiently and much earlier than predicted, posing new challenges to models of galaxy formation. Drawing on results mainly from the JWST FRESCO and PANORAMIC surveys, I will present recent progress in characterizing these massive systems — from heavily dust-obscured star-forming galaxies to already evolved populations within the first billion years — and discuss new insights from ALMA and NOEMA follow-up observations. Some sources initially identified as extremely massive galaxies are now found to belong to the so-called “Little Red Dots,” illustrating how multi-wavelength data can refine our view of early galaxy populations. I will also touch on HST-dark galaxies (known pre-JWST) and the newly reported JWST/NIRCam-dark examples that may trace previously hidden phases of rapid buildup. Together, these studies offer a first glimpse into how the first generation of massive galaxies formed bigger, faster, and earlier than expected.