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
- 1The University of Tokyo
- 2National Astronomical Observatory of Japan
- 3SOKENDAI (The Graduate University for Advanced Studies)
Abstract
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 H β / 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 Ly α (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
@article{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},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/aea6cc},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea6cc},
note = {CC BY 4.0},
}
RIS
TY - JOUR
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 - 2026/10/21
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aea6cc
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aea6cc
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 H β / 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 Ly α (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.
SN - 0004-637X
SN - 1538-4357
ER -