Work

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

Year: 2026

Type: article

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.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/aea6cc

Authors: Minami Nakane, Masami Ouchi

Institutions: The University of Tokyo, The Graduate University for Advanced Studies, SOKENDAI, National Astronomical Observatory of Japan

Language: English

Topic: Galaxies: Formation, Evolution, Phenomena

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $4,499

Funders: National Aeronautics and Space Administration, Space Telescope Science Institute