Astrophysics Colloquium: Galaxies in the Reionization Era: New Insight from JWST

Abstract: Over the past few years, deep infrared images and spectra from JWST have pushed the cosmic frontier back to just 300 million years after the Big Bang, delivering the first large sample of galaxies at redshifts 7<z<14. Sometime in this redshift window the hydrogen in the intergalactic medium transitioned from mostly neutral to ionized. The emergence of the first detailed spectra of z>7 galaxies have begun to sharpen our understanding of this process of reionization, while also providing a glimpse of the physical nature of early galaxies. The spectral features we are detecting at z>7 are unlike what has been seen at lower redshifts, revealing a metal poor population of low mass galaxies with bursty star formation histories. New data are indicating that this burst phase often coincides with hard ionizing sources of unknown origin, very dense star cluster complexes, very massive stars, and abundance patterns rarely seen in galaxies but identical to those of globular cluster stars. In this talk, I will review the latest progress in our understanding of reionization and early galaxies, then discuss several of the surprises that have emerged in the first datasets from JWST.