JWST Absorption-Line Analysis of UV-Bright Galaxies at z=7.2−10.6: Early Chemical Enrichment Traced by C, O, Mg, Al, Si, and Fe
Abstract
We investigate UV absorption lines tracing cool gas in eight bright (−21.9 < MUV < −20.5) galaxies at z=7.2−10.6 using deep archival JWST/NIRSpec medium-resolution spectra. The eight galaxies were homogeneously selected based on wavelength coverage and data quality from 362 galaxies at z>7 available to date, and all eight were observed as part of the SPURS program. We identify multiple absorption lines of low-ionization species (LIS) in five galaxies, while the remaining three show only one or no significant detections. The average LIS equivalent widths EWLIS indicate weaker absorption lines in compact (re≲100 pc) galaxies with high LHβ/LUV and ΣSFR, suggestive of absorption-line suppression due to intense star formation or nuclear activity. We simultaneously fit multiple LIS lines, accounting for both covering fraction Cf and column density N, and find that the five galaxies follow the local Cf-N relation. Through the LIS-line fitting, we derive chemical abundance ratios. The five galaxies have abundance ratios similar to those of damped Lyα (DLA) systems at z∼5−7 in the [Si/O]-[C/O] and [Fe/Si]-[Al/Si] planes, suggesting that their absorbing gas is similar to that of DLAs. We find that two galaxies at z∼7 are already highly Fe-enriched, with [Fe/Si]≃−0.2, near the solar abundance ratio. While the high Fe enrichment may originate from early Type-Ia supernovae (SNe Ia) or pair-instability supernovae (PISNe), these two galaxies also show [Al/Si]∼0, with no signature of the strong odd-even effect expected from PISNe, in which odd-Z elements are suppressed relative to even-Z elements, favoring SNe Ia.
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BibTeX
@misc{nakane2026jwst,
title = {{JWST Absorption-Line Analysis of UV-Bright Galaxies at $z=7.2-10.6$: Early Chemical Enrichment Traced by C, O, Mg, Al, Si, and Fe}},
author = {Minami Nakane and Masami Ouchi},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2606.08782},
eprint = {2606.08782},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.08782},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - JWST Absorption-Line Analysis of UV-Bright Galaxies at z=7.2−10.6: Early Chemical Enrichment Traced by C, O, Mg, Al, Si, and Fe
AU - Minami Nakane
AU - Masami Ouchi
PY - 2026
DA - 2026/08/31
PB - arXiv
DO - 10.48550/arxiv.2606.08782
UR - https://arxiv.org/abs/2606.08782
AB - We investigate UV absorption lines tracing cool gas in eight bright (−21.9 < M_UV < −20.5) galaxies at z=7.2−10.6 using deep archival JWST/NIRSpec medium-resolution spectra. The eight galaxies were homogeneously selected based on wavelength coverage and data quality from 362 galaxies at z>7 available to date, and all eight were observed as part of the SPURS program. We identify multiple absorption lines of low-ionization species (LIS) in five galaxies, while the remaining three show only one or no significant detections. The average LIS equivalent widths EW_LIS indicate weaker absorption lines in compact (r_e≲100 pc) galaxies with high L_Hβ/L_UV and Σ_SFR, suggestive of absorption-line suppression due to intense star formation or nuclear activity. We simultaneously fit multiple LIS lines, accounting for both covering fraction C_f and column density N, and find that the five galaxies follow the local C_f-N relation. Through the LIS-line fitting, we derive chemical abundance ratios. The five galaxies have abundance ratios similar to those of damped Lyα (DLA) systems at z∼5−7 in the [Si/O]-[C/O] and [Fe/Si]-[Al/Si] planes, suggesting that their absorbing gas is similar to that of DLAs. We find that two galaxies at z∼7 are already highly Fe-enriched, with [Fe/Si]≃−0.2, near the solar abundance ratio. While the high Fe enrichment may originate from early Type-Ia supernovae (SNe Ia) or pair-instability supernovae (PISNe), these two galaxies also show [Al/Si]∼0, with no signature of the strong odd-even effect expected from PISNe, in which odd-Z elements are suppressed relative to even-Z elements, favoring SNe Ia.
ER -