# JADES: Detecting [OIII]$λ4363$ Emitters and Testing Strong Line Calibrations in the High-$z$ Universe with Ultra-deep JWST/NIRSpec Spectroscopy up to $z \sim 9.5$

**Authors:** Isaac H. Laseter, Michael V. Maseda, Mirko Curti, Roberto Maiolino, Francesco D'Eugenio, Alex J. Cameron, Tobias J. Looser, Santiago Arribas, William M. Baker, Rachana Bhatawdekar, Kristan Boyett, Andrew J. Bunker, Stefano Carniani, Stephane Charlot, Jacopo Chevallard, Emma Curtis-lake, Eiichi Egami, Daniel J. Eisenstein, Kevin Hainline, Ryan Hausen  
**arXiv:** [2306.03120](https://arxiv.org/abs/2306.03120)  
**Date:** 2023-06-05  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.03120v1/

## Key points

- 10 new detections of the [OIII]$\lambda 4363$ auroral line up to a redshift of $z\sim 9.5$
- Ultra-deep spectroscopic observations using JWST/NIRSpec MSA instrument as part of JADES
- Determination of electron temperatures and oxygen abundances using direct T$_e$ method
- Comparison of results against locally calibrated strong-line diagnostics and high-redshift calibrations
- Calibrations fail to match JADES sample, indicating need for revision at high redshifts
- Ineffectiveness of certain line-ratios (R2 and O3O2) as metallicity diagnostics at high redshifts
- Tentative flattening in other strong-line ratios (R3 and R23) used as metallicity indicators in local galaxies
- Proposal and testing of alternative diagnostic based on different combination of R3 and R2 with higher dynamic range
- Higher ionization/excitation ratios in their galaxies compared to local galaxies
- Median rest-frame EWs(H$\beta$) about two times less than those used for local calibrations
- Discrepancy in EW combined with high ionization raises questions about production of [OIII]$\lambda 4363$
- Novel detections providing insights into metallicity diagnostics at high redshifts
- Findings warrant revision of existing calibrations and development of new diagnostic tools

## Summary

In this study, the authors present 10 new detections of the [OIII]$\lambda 4363$ auroral line up to a redshift of $z\sim 9.5$. These detections were made using ultra-deep spectroscopic observations from the JWST/NIRSpec MSA instrument as part of the JWST Advanced Deep Extragalactic Survey (JADES). The authors leverage these deep observations to determine electron temperatures and oxygen abundances using the direct T$_e$ method. To validate their measurements, the authors compare their results against a suite of locally calibrated strong-line diagnostics and recent high-redshift calibrations. Surprisingly, they find that these calibrations fail to simultaneously match their JADES sample, indicating a need for a self-consistent revision of these calibrations for the high-redshift Universe. The authors also investigate the effectiveness of certain line-ratios, such as R2 and O3O2, as metallicity diagnostics and degeneracy breakers in the high-redshift Universe. They find weak dependence between these line-ratios and metallicity, suggesting that they are ineffective in accurately determining metallicity at high redshifts. Additionally, they observe tentative flattening in other strong-line ratios (R3 and R23) that are commonly used as metallicity indicators in local galaxies. This indicates potential difficulties when applying these ratios as metallicity indicators in the high-redshift Universe. To address these challenges, the authors propose and test an alternative diagnostic based on a different combination of R3 and R2 with a higher dynamic range. They find reasonably good agreement with the JWST sample at low metallicity using this alternative diagnostic. Furthermore, the authors analyze additional properties of their sample. They find that their galaxies demonstrate higher ionization/excitation ratios compared to local galaxies with rest-frame equivalent widths (EWs) of H$\beta$ ranging from approximately 200 to 300 Angstroms. However, they also observe that the median rest-frame EWs(H$\beta$) of their sample are about two times less than those of the galaxies used for the local calibrations. This discrepancy in EW combined with the high ionization of their galaxies raises questions about the production of [OIII]$\lambda 4363$ in the high-redshift Universe, highlighting the need for further investigation into factors affecting its production. Overall, this study presents novel detections of [OIII]$\lambda 4363$ auroral lines up to a redshift of $z\sim 9.5$, providing valuable insights into metallicity diagnostics and degeneracy breakers at high redshifts. The authors' findings warrant a revision of existing calibrations and emphasize importance developing new diagnostic tools for accurately determining metallicity in high redshifts Universe.