What question did this study set out to answer?

This research aims to measure the metallicity of early galaxies at redshift z≈10 and investigate their star formation histories.

March 21, 2026

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

Key Points

This research aims to measure the metallicity of early galaxies at redshift z≈10 and investigate their star formation histories.
Utilized new high-quality spectroscopic observations of doublet lines and auroral lines.
Analyzed 11 galaxies in the sample at redshifts z=9.3-10.0.
Calculated T_e-based metallicity and mass-metallicity relations using optical emission lines.
Expanded wavelength coverage for improved spectral analysis beyond traditional limits.
Detected high ionisation fields and electron temperatures in the interstellar medium of all studied galaxies.
Extended metallicity measurements indicate typical values of 12+log(O/H) between 7.1 - 8.3, reflecting 3-50% solar metallicity.
Observed a gradual decline in the mass-metallicity relation at higher redshifts, with implications for earlier cosmic star formation patterns.
Established an empirical relation for future studies involving mass and metallicity at high redshifts.

Abstract

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, łambdałambda 4959, 5007 doublet and resolve the auroral, łambda 4363 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+łog Prism observations from the archive. In particular, we extend the wavelength coverage beyond the standard pipeline cut-off (5. 3μm) 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 iii ̊m (O/H) = 7. 1 - 8. 3 (3--50% solar), consistent with previous strong-line diagnostics based on) and with evidence of bursty star formation on 10, Myr versus 100, Myr timescales (log_ () ≈ 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 data at high redshifts. We derive an empirical relation for M_̊m UV 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 = SFR_̊m Hβ/M_⋆ = 38, Gyr -1 10 ̊m SFR_ 10 /SFR_ 100 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.

Bookmark

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

Key Points

Abstract

Cite This Study

Also Consider

Also Consider