2025/06/18 by Pollock, Clara L., Gottumukkala, Rashmi, Heintz, Kasper E. +15 · 2 citations
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2506.15779
The mass assembly and chemical enrichment of the first galaxies provide key insights into their star-formation histories and the earliest stellar populations at cosmic dawn. Here we compile and utilize new, high-quality spectroscopic JWST/NIRSpec Prism observations from the JWST archive. We extend the wavelength coverage beyond the standard pipeline cutoff up to 5.5μm, enabling a detailed examination of the rest-frame optical emission-line properties for galaxies at z≈ 10. The improved calibration allows us to detect Hβ and the [OIII]λλ4959,5007 doublet and resolve the auroral [OIII]λ4363 line for the 11 galaxies in our sample (z=9.3-10.0) to obtain direct Te-based metallicity measurements. We find that all galaxies show high ionisation fields and electron temperatures, with derived metallicities in the range 12+log \rm (O/H) = 7.1 - 8.3, consistent with previous strong-line diagnostics at high-z. We derive an empirical relation for M\rm UV and 12+log(O/H) at z≈ 10, useful for future higher-z studies, and show that the sample galaxies are `typical' star-forming galaxies though with relatively high specific star-formation rates and with evidence for bursty star formation. Combining the rest-frame optical line analysis and detailed UV to optical SED modelling, we determine the mass-metallicity relation and the fundamental-metallicity relation of the sample, pushing the redshift frontier of these measurements to z=10. These results, together with literature measurements, point to a gradually decreasing MZR at higher redshifts, with a break in the FMR at z≈ 3, decreasing to metallicities ≈ 3× lower at z=10 than observed during the majority of cosmic time at z=0-3, likely caused by massive pristine gas inflows diluting the observed metal abundances during early galaxy assembly at cosmic dawn.