James Webb Space Telescope Feed Post

Harvard ADS: GA-NIFS: An extremely nitrogen-loud and chemically stratified galaxy at z\sim 5.55

Paper abstract: We report the chemical abundance pattern of GS\_3073, a galaxy at z=5.55 which was previously confirmed to host an overmassive active black hole, by leveraging the detection of about 40 emission lines, combining JWST/NIRSpec observations and ground-based (VLT/VIMOS) data. By using rest-frame UV emission lines, which trace high-density (~ 10^5~{\rm cm}^{-3}) and highly ionized gas, we derived an abundance ratio of \rm log(N/O) = 0.46^{+0.12}_{-0.09}. At an estimated metallicity of 0.2~Z_{\odot}, this is the most extreme nitrogen-rich object found by JWST thus far. In comparison, the relative carbon abundance derived from the rest-frame UV emission lines is \rm log(C/O) = -0.30^{+0.12}_{-0.09}, which is not significantly higher than those in local galaxies and stars with similar metallicities. We also detected coronal lines, including [FeVII]\lambda 6087 and potentially [FeXIV]\lambda 5303. We inferred a high Fe abundance of \rm [Fe/O] \gtrsim 0.1. Overall, the chemical abundance pattern of GS\_3073 is compatible with enrichment by super-massive stars with M_* \gtrsim 1000~M_\odot, ejecta from asymptotic giant branch (AGB) stars, or winds from Wolf-Rayet (WR) stars, although the WR scenario is less likely. Interestingly, when using optical emission lines which trace lower density (~ 10^3~{\rm cm}^{-3}) and lower ionization gas, we found a sub-solar N/O ratio. We interpret the difference in N/O derived from UV lines and optical lines as evidence for a stratified system, where the inner and denser region is both more chemically enriched and more ionized. Taking this luminous, well-studied system as a benchmark, our results suggest that nitrogen loudness in high-z galaxies is confined to the central, dense, and highly ionized region of the galaxy, while the bulk of the galaxy evolves more normally.