The Department of Astronomy 2025-2026 Colloquium Series Presents:

"CECILIA: A Benchmark Sample for Studying Galaxy Enrichment at Cosmic Noon"

A significant fraction of all stars in the Universe today formed during a 2-3 Gyr period around z~1-3, when both cosmic star-formation rate density and quasar number density reached their peak values. As a result, this epoch---commonly known as "Cosmic Noon"---represents a key phase in galaxy evolution and has been studied extensively over the last decade. In recent years, our ability to characterize galaxies at these redshifts has improved dramatically thanks to the capabilities of JWST, which has made it possible to detect extremely faint emission lines sensitive to a variety of physical properties, including gas temperature and hard ionizing radiation. I will review recent results from CECILIA, a Cycle 1 JWST program that obtained ultra-deep (30-hour) spectra of typical star-forming galaxies at Cosmic Noon, extending down to relatively low-mass (10^7.5 solar masses) Milky Way progenitor analogues that have <5% solar O/H in their interstellar medium. These findings include one of the most detailed analyses to date of multi-element chemistry in the distant Universe, as well as intriguing evidence for differences in these galaxies' massive star populations and the impact of stellar feedback. I will also discuss how deep spectroscopic samples like CECILIA are leading to new best practices for measuring the metallicity of nascent galaxies and highlight future prospects for combining these unique data with other ground- and space-based campaigns.