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Abstract Abundances of chemical elements in the interstellar and circumgalactic media of high-redshift galaxies offer important constraints on the nucleosynthesis by early generations of stars. Damped Lyαabsorbers (DLAs) in spectra of high-redshift background quasars are excellent sites for obtaining robust measurements of element abundances in distant galaxies. Past studies of DLAs at redshiftsz> 4 have measured abundances of ≲0.01 solar. Here we report the discovery of a DLA atz= 4.7372 with an exceptionally high degree of chemical enrichment. We estimate the Hicolumn density in this absorber to be log (NH I/cm−2) = 20.48 ± 0.15. Our analysis shows unusually high abundances of carbon and oxygen ([C/H] = 0.88 ± 0.17, [O/H] = 0.71 ± 0.16). Such a high level of enrichment a mere 1.2 Gyr after the Big Bang is surprising because of insufficient time for the required amount of star formation. To our knowledge, this is the first supersolar absorber found atz> 4.5. We find the abundances of Si and Mg to be [Si/H] = and [Mg/H] = , confirming the metal-rich nature of this absorber. By contrast, Fe shows a much lower abundance ([Fe/H] = ). We discuss implications of our results for galactic chemical evolution models. The metallicity of this absorber is higher than that of any other known DLA and is >2 orders of magnitude above predictions of chemical evolution models and theNH I-weighted mean metallicity from previous studies atz> 4.5. The relative abundances (e.g., [O/Fe] = 2.29 ± 0.05, [C/Fe] = 2.46 ± 0.08) are also highly unusual compared to predictions for enrichment by early stars.
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This content will become publicly available on August 1, 2026
High-pressure reduction of carbon dioxide in reactive liquid mixtures
Density-functional theory based molecular-dynamics simulations were used to investigate high-pressure chemical reactions in liquid mixtures of CO2 with several elements (Si, Mn, and Fe) at high temperatures of 2000–3000 K. Our ab initio simulations indicate that these reactant elements can reduce CO2 to C at high pressures (20 GPa) leading to the formation of C-C chains, with Si by far the most effective carbon-reducing agent. A combined chemical analysis using Bader charge analysis and crystal orbital Hamilton population (COHP) on simulation snapshots shows that significant charge transfer from the reducing element to the C atoms creates instability in the C-O covalent bonds. COHP analysis further shows that Mn/Fe-O and Mn/Fe-C bonding interactions are weaker compared to the Si counterparts. These results further our understanding of the redox chemistry of CO2 at conditions relevant to planetary mantle interiors and demonstrate the effectiveness of high pressure in the reduction of CO2 directly to solid carbon.
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- Award ID(s):
- 2205521
- PAR ID:
- 10631645
- Publisher / Repository:
- APS
- Date Published:
- Journal Name:
- Physical Review B
- Volume:
- 112
- Issue:
- 5
- ISSN:
- 2469-9950
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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