Novel z ∼ 10 auroral line measurements extend the gradual offset of the fundamental metallicity relation deep into the first gigayear of cosmic time

article Novel z ∼ 10 auroral line measurements extend the gradual offset of the fundamental metallicity relation deep into the first gigayear of cosmic time published yes Clara L. Pollock author Rashmi Gottumukkala author Kasper E. Heintz author Gabriel B. Brammer author Guido Roberts-Borsani author Pascal A. Oesch author Joris Witstok author Karla Z. Arellano-Córdova author Fergus Cullen author Dirk Scholte author Chamilla Terp author Lucie Rowland author Albert Sneppen author Kei Ito author Francesco Valentino author Jorryt J Matthee author 7439a258-f3c0-11ec-9501-9df22fe067200000-0003-2871-127X Darach Watson author Sune Toft author JoMa department 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 utilise new, high-quality spectroscopic JWST/NIRSpec Prism observations from the JWST archive. In particular, we extend the wavelength coverage beyond the standard pipeline cut-off (5.3 μm) up to 5.5 μm, which enables for the first time a detailed examination of the rest-frame optical emission-line properties for galaxies at z ≈ 10. Crucially, the improved calibration allows us to detect Hβ and the [O III] λλ4959, 5007 doublet and resolve the auroral [O III] λ4363 line for the 11 galaxies in our sample (z = 9.3 − 10.0) to obtain direct Te-based metallicity measurements. We find that the interstellar medium (ISM) of all galaxies shows high ionisation fields and electron temperatures, with derived metallicities in the range 12 + log(O/H) = 7.1 − 8.3 (3–50% solar), consistent with previous strong-line diagnostics based on JWST data at high redshifts. We derive an empirical relation for MUV and 12 + log(O/H) at z ≈ 10, useful for future higher-redshift studies, and show that the sample galaxies are ‘typical’ star-forming galaxies though with relatively high specific star formation rates (median sSFR = SFRHβ/M★ = 38 Gyr−1) and with evidence of bursty star formation on 10 Myr versus 100 Myr timescales (log10(SFR10/SFR100)≈0.7). Combining the rest-frame optical line analysis and detailed UV to optical spectro-photometric modelling, we determine the mass-metallicity relation (MZR) and the fundamental metallicity relation (FMR) of the sample, pushing the previous 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 in galaxies 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. https://research-explorer.ista.ac.at/download/22815/22874/2026_AstronomyAstrophysics_Pollock.pdf application/pdfno EDP Sciences2026 eng Astronomy & Astrophysics 0004-6361 1432-0746 2506.1577910.1051/0004-6361/202556032 708 Pollock CL, Gottumukkala R, Heintz KE, et al. Novel z ∼ 10 auroral line measurements extend the gradual offset of the fundamental metallicity relation deep into the first gigayear of cosmic time. Astronomy & Astrophysics. 2026;708. doi:<a href="https://doi.org/10.1051/0004-6361/202556032">10.1051/0004-6361/202556032</a> Pollock, C. L., Gottumukkala, R., Heintz, K. E., Brammer, G. B., Roberts-Borsani, G., Oesch, P. A., … Toft, S. (2026). Novel z ∼ 10 auroral line measurements extend the gradual offset of the fundamental metallicity relation deep into the first gigayear of cosmic time. Astronomy & Astrophysics. EDP Sciences. <a href="https://doi.org/10.1051/0004-6361/202556032">https://doi.org/10.1051/0004-6361/202556032</a> Pollock, Clara L., et al. “Novel z ∼ 10 Auroral Line Measurements Extend the Gradual Offset of the Fundamental Metallicity Relation Deep into the First Gigayear of Cosmic Time.” Astronomy & Astrophysics, vol. 708, A203, EDP Sciences, 2026, doi:<a href="https://doi.org/10.1051/0004-6361/202556032">10.1051/0004-6361/202556032</a>. C. L. Pollock et al., “Novel z ∼ 10 auroral line measurements extend the gradual offset of the fundamental metallicity relation deep into the first gigayear of cosmic time,” Astronomy & Astrophysics, vol. 708. EDP Sciences, 2026. C.L. Pollock, R. Gottumukkala, K.E. Heintz, G.B. Brammer, G. Roberts-Borsani, P.A. Oesch, J. Witstok, K.Z. Arellano-Córdova, F. Cullen, D. Scholte, C. Terp, L. Rowland, A. Sneppen, K. Ito, F. Valentino, J.J. Matthee, D. Watson, S. Toft, Astronomy & Astrophysics 708 (2026). Pollock CL, Gottumukkala R, Heintz KE, Brammer GB, Roberts-Borsani G, Oesch PA, Witstok J, Arellano-Córdova KZ, Cullen F, Scholte D, Terp C, Rowland L, Sneppen A, Ito K, Valentino F, Matthee JJ, Watson D, Toft S. 2026. Novel z ∼ 10 auroral line measurements extend the gradual offset of the fundamental metallicity relation deep into the first gigayear of cosmic time. Astronomy & Astrophysics. 708, A203. Pollock, Clara L., Rashmi Gottumukkala, Kasper E. Heintz, Gabriel B. Brammer, Guido Roberts-Borsani, Pascal A. Oesch, Joris Witstok, et al. “Novel z ∼ 10 Auroral Line Measurements Extend the Gradual Offset of the Fundamental Metallicity Relation Deep into the First Gigayear of Cosmic Time.” Astronomy & Astrophysics. EDP Sciences, 2026. <a href="https://doi.org/10.1051/0004-6361/202556032">https://doi.org/10.1051/0004-6361/202556032</a>. 228152026-09-06T22:01:56Z2026-09-09T12:07:45Z