Tracing Extreme Star Formation: Chemical Abundances in Early Galaxies Across Cosmic Time
Speaker: Yuki Isobe (Cambridge University)
Abstract:
Chemical abundance ratios in the interstellar medium of galaxies trace the accumulated contributions of stars with varying masses, serving as key indicators of early star formation. In particular, nitrogen-to-oxygen (N/O) and iron-to-oxygen (Fe/O) ratios have generally been thought to increase with galaxy age: massive stars initially eject oxygen via core-collapse supernovae, while later contributions from lower-mass stars enhance nitrogen and iron abundances. However, this standard evolutionary scenario has been challenged by recent spectroscopic observations using the James Webb Space Telescope (JWST) and large ground-based telescopes. This talk will review these findings across cosmic time, particularly z~0 extremely metal-poor emission-line galaxies with ~solar Fe/O ratios and z>5 galaxies with supersolar N/O ratios. I will also discuss a connection between nitrogen enhancement, dense gas, and active galactic nuclei, providing new insights into early chemical enrichment, clustered star formation, and massive black hole seeding in the early Universe.