Galaxy Protoclusters as Drivers of Cosmic Reionization: II. Te-Based Metallicities of Lyman-α Emitters
Abstract
Context. Protoclusters at reionization are thought to host a significant fraction of the cosmic star formation rate density, making them crucial for the timing and topology of reionization. The gas-phase metallicity, a key tracer of galaxy evolutionary stage, can now be measured directly in the early Universe with JWST. Aims. We measure the gas-phase metallicity of Lyman-α emitters (LAEs) in the LAGER-z7OD1 protocluster at z≈6.93 via the direct (Te-based) method using the [O III]λ4363 auroral line, and combine it with stellar masses to constrain the mass-metallicity relation (MZR) in dense environments. Methods. We use JWST/NIRSpec MSA G395H spectroscopy, derive metallicities with self-consistent analytic prescriptions, and propagate the dust-extinction uncertainty into an asymmetric error budget via Monte Carlo simulations based on the observed Balmer decrements. Stellar masses come from BEAGLE SED fitting of JWST/NIRCam and UltraVISTA photometry. Results. We obtain five secure [O III]λ4363 detections and one upper limit, with 12+log(O/H) ≈ 7.2-8.0. The weighted spectral stack yields 12+log(O/H) = 7.76+0.06−0.05, ~0.26 dex higher than stacks of LAEs at similar redshifts from JWST surveys. However, the MZR fit gives a slope γ = 0.232 +/- 0.214 and normalization Z0 = 7.888 +/- 0.199, placing our sources below the established MZR of normal galaxies and recent protocluster baselines at z∼5−7. Conclusions. The higher metallicity relative to general LAEs suggests accelerated assembly driven by the overdensity, while the offset below the MZR points to a complex interplay between mass build-up and gas accretion. Since we target actively star-forming LAEs, we are likely capturing a phase of pristine gas inflow from the intergalactic medium that fuels star formation but dilutes the interstellar media of these protocluster members.
Related
- Diverse Metallicities in Protoclusters at z ∼ 3.4 detected by Deep Learning
- Diverse Metallicities in Protoclusters at z ~ 3.4 detected by Deep Learning
- The multiphase circumgalactic medium in the epoch of reionization: CII and CIV absorbers around [OIII] emitters
- An Updated Characterization of Luminous Lyα emitters at the End of Reionization
- The Multiphase CGM in the Epoch of Reionization: CII and CIV absorbers around [OIII] Emitters
BibTeX
@misc{moyasierralta2026galaxy,
title = {{Galaxy Protoclusters as Drivers of Cosmic Reionization: II. Te-Based Metallicities of Lyman-α Emitters}},
author = {C. Moya-Sierralta and C. L. Martin and L. F. Barrientos and L. Infante and J. González-López and W. Hu and A. L. Faisst and Y. Harikane and A. M. Koekemoer and S. Malhotra and M. Ouchi and Z. Peng and J. Rhoads and J. Wang and J. R. Weaver and I. Wold and J. Yang and Z. Zheng},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.01811},
eprint = {2610.01811},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.01811},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Galaxy Protoclusters as Drivers of Cosmic Reionization: II. Te-Based Metallicities of Lyman-α Emitters
AU - C. Moya-Sierralta
AU - C. L. Martin
AU - L. F. Barrientos
AU - L. Infante
AU - J. González-López
AU - W. Hu
AU - A. L. Faisst
AU - Y. Harikane
AU - A. M. Koekemoer
AU - S. Malhotra
AU - M. Ouchi
AU - Z. Peng
AU - J. Rhoads
AU - J. Wang
AU - J. R. Weaver
AU - I. Wold
AU - J. Yang
AU - Z. Zheng
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.01811
UR - https://arxiv.org/abs/2610.01811
AB - Context. Protoclusters at reionization are thought to host a significant fraction of the cosmic star formation rate density, making them crucial for the timing and topology of reionization. The gas-phase metallicity, a key tracer of galaxy evolutionary stage, can now be measured directly in the early Universe with JWST. Aims. We measure the gas-phase metallicity of Lyman-α emitters (LAEs) in the LAGER-z7OD1 protocluster at z≈6.93 via the direct (T_e-based) method using the [O III]λ4363 auroral line, and combine it with stellar masses to constrain the mass-metallicity relation (MZR) in dense environments. Methods. We use JWST/NIRSpec MSA G395H spectroscopy, derive metallicities with self-consistent analytic prescriptions, and propagate the dust-extinction uncertainty into an asymmetric error budget via Monte Carlo simulations based on the observed Balmer decrements. Stellar masses come from BEAGLE SED fitting of JWST/NIRCam and UltraVISTA photometry. Results. We obtain five secure [O III]λ4363 detections and one upper limit, with 12+log(O/H) ≈ 7.2-8.0. The weighted spectral stack yields 12+log(O/H) = 7.76^+0.06_−0.05, ~0.26 dex higher than stacks of LAEs at similar redshifts from JWST surveys. However, the MZR fit gives a slope γ = 0.232 +/- 0.214 and normalization Z_0 = 7.888 +/- 0.199, placing our sources below the established MZR of normal galaxies and recent protocluster baselines at z∼5−7. Conclusions. The higher metallicity relative to general LAEs suggests accelerated assembly driven by the overdensity, while the offset below the MZR points to a complex interplay between mass build-up and gas accretion. Since we target actively star-forming LAEs, we are likely capturing a phase of pristine gas inflow from the intergalactic medium that fuels star formation but dilutes the interstellar media of these protocluster members.
ER -