Unveiling Early Cosmic Enrichment: Direct Metallicities in z>6 Galaxies from Deep JWST Spectroscopy

What are the metal contents of galaxies, how quickly did they form, are strong-line diagnostics sufficiently robust to measure them? JWST has extended the frontier of galaxy metallicity studies, enabling measurements of strong diagnostics lines out to z12. However, tracing the build up of metals across the first billion years remains extremely challenging and current constraints are sorely lacking. At z>6, simulations yield contrasting predictions due to different feedback physics, while observationally only 17 objects observed with JWST have benefited from gold- standard, electron temperature-based metallicities. The vast majority of objects have instead relied on inferences using uncertain Oxygen and Balmer strong-line calibrations anchored to small numbers of 2<z<9>6 galaxies in the GOODS fields, through deep NIRSpec G395M/F290LP spectroscopy of [O III]4963 and [O II]3728,3730. With a ~4x increase in detections compared to current samples, we will: (i) Establish the most robust R23 and O32 calibrations to date, and explore [Ne III]-based indices for applications at z>10. (ii) Utilize those calibrations to obtain robust metallicities in >500 sources at z613 for mass-metallicity characterizations. (iii) Examine evolutionary trends and characterize the intrinsic scatter of galaxy metallicities over the first billion years.</z<9>