# EIGER II. first spectroscopic characterisation of the young stars and ionised gas associated with strong H$β$ and [OIII] line-emission in galaxies at z=5-7 with JWST

**Authors:** Jorryt Matthee, Ruari Mackenzie, Robert A. Simcoe, Daichi Kashino, Simon J. Lilly, Rongmon Bordoloi, Anna-Christina Eilers  
**arXiv:** [2211.08255](https://arxiv.org/abs/2211.08255)  
**Date:** 2022-11-15  
**Summary page:** https://www.summarizepaper.com/en/paper/2211.08255v1/

## Key points

- Study presents emission-line measurements and interpretations for 117 [OIII] emitting galaxies at redshifts 5.33 to 6.93
- Measurements obtained using deep JWST/NIRCam wide field slitless spectroscopic observations
- Focus on the $z=6.3$ quasar J0100+2802 as part of the EIGER survey
- Integration time for observation was 9.7 hours, covering wavelength range of 3-4 microns
- Detect 133 [OIII] doublets in galaxies, merging pairs within approximately 10 kiloparsecs and 600 kilometers per second due to small scale clustering excess
- H$\beta$ detected in 68 galaxies, H$\gamma$ detected in two galaxies
- Explored characteristics of these galaxies: UV luminosity M$_{\rm UV}$ around -19.7, mass around $10^8$ solar masses
- Equivalent widths (EWs) of H$\beta$ and [OIII] lines approximately 1000 Angstroms (up to 3000 Angstroms), indicating highly excited interstellar medium and low dust attenuations; high EWs rare in local Universe but ubiquitous at redshifts around 6 based on measured number densities
- Stacked spectrum analysis reveals presence of H$\gamma$, [OIII] lines, and electron temperature of $2\times10^4$
- Galaxies typically dust and metal poor with high production efficiency of ionizing photons ($\xi_{\rm ion}=10^{25.6}~{\rm Hz~erg^{-1}}$
- Evidence for strong mass-metallicity relation consistent with theoretical simulations
- Enhanced [OIII] output compared to lower redshift galaxies despite decline in cosmic star formation rate at z~6, resulting in significantly higher [OIII] luminosity density than z~2
- JWST's [OIII] emission-line surveys highly efficient for tracing galaxy density during epoch of reionization
- Detailed measurements and interpretations contribute to understanding of properties and evolution of high redshift galaxies.

## Summary

In this study, the authors present emission-line measurements and physical interpretations for a sample of 117 [OIII] emitting galaxies at redshifts ranging from 5.33 to 6.93. These measurements were obtained using the first deep JWST/NIRCam wide field slitless spectroscopic observations, with a focus on the $z=6.3$ quasar J0100+2802 as part of the EIGER survey. The integration time for this observation was 9.7 hours, covering a wavelength range of 3-4 microns. The authors detect 133 [OIII] doublets in these galaxies, but they merge pairs within approximately 10 kiloparsecs and 600 kilometers per second due to their small scale clustering excess. Additionally, H$\beta$ is detected in 68 galaxies and H$\gamma$ is detected in two galaxies. The characteristics of these galaxies are explored in detail: they have a UV luminosity M$_{\rm UV}$ around -19.7 (ranging from -17.7 to -22.3) and a mass around $10^8$ solar masses (ranging from $10^{6.8}$ to $10^{9.8}$ solar masses). The equivalent widths (EWs) of H$\beta$ and [OIII] lines are approximately 1000 Angstroms (up to 3000 Angstroms), indicating highly excited interstellar medium ([OIII]/H$\beta\approx6$) and low dust attenuations; interestingly, such high EWs are rare in the local Universe but appear to be ubiquitous at redshifts around 6 based on measured number densities. The stacked spectrum analysis reveals the presence of H$\gamma$, [OIII] lines and an electron temperature of $2\times10^4$, suggesting that these galaxies are typically dust and metal poor with a high production efficiency of ionizing photons ($\xi_{\rm ion}=10^{25.6}~{\rm Hz~erg^{-1}}$. Furthermore, there is evidence for a strong mass-metallicity relation in these galaxies which is consistent with theoretical simulations; this combination leads to an enhanced [OIII] output compared to lower redshift galaxies despite the overall decline in cosmic star formation rate at z~6 resulting in significantly higher [OIII] luminosity density than z~2 . Overall, this study demonstrates that JWST's [OIII] emission-line surveys are highly efficient for tracing galaxy density during the epoch of reionization; its detailed measurements and physical interpretations contribute greatly to our understanding of properties and evolution of high redshift galaxies.