On the Importance of the Intergalactic and Circumgalactic Medium Enrichment in Determining Chemical Abundances during the First 600 Myr
- 1Sam Houston State University
- 2University of Minnesota
Abstract
JWST observations show that galaxies at z > 8 exhibit a wide range of carbon-to-oxygen (C/O) ratios at fixed metallicity and systematically elevated nitrogen-to-oxygen (N/O) ratios compared to local galaxies. Proposed explanations include finely tuned star formation histories (SFHs), differential or pristine inflows, top- or bottom-heavy initial mass functions (IMFs), or enrichment from Wolf–Rayet stars, supermassive stars (SMSs), or Population III (Pop III) stars. The observed abundances reflect both in situ production tied to the SFHs and earlier pre-enrichment of the intergalactic and circumgalactic medium (IGM/CGM), which supply the gas inflow that fuels star formation. At such early epochs, SFHs are necessarily brief, and sustained star formation requires inflows to dominate over outflows, making the chemical state of the IGM/CGM especially important. We develop a chemical-evolution model that incorporates (1) enrichment of the IGM/CGM by multiple sources and (2) the observed SFHs of high-redshift galaxies. Applying this model to eight galaxies at z > 8, we find that only specific pre-enrichment scenarios reproduce their observed abundance ratios. For example, the low C/O and high N/O ratios measured in GN-z11 and CEERS-1019 require an IGM/CGM enriched by supermassive stars (SMSs) and pre-enriched to an oxygen metallicity of ∼10 ⁻⁵ of the solar value. We also find that the log ( N / O ) versus 12 + log ( O / H ) plane provides more stringent constraints on enrichment pathways than the log ( C / O ) versus 12 + log ( O / H ) plane. Overall, our results highlight the crucial role of IGM/CGM chemical composition in chemical-evolution models at z > 8 and underscore the significant influence of SMSs on early carbon, nitrogen, and oxygen abundances.
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BibTeX
@article{citro2026importance,
title = {{On the Importance of the Intergalactic and Circumgalactic Medium Enrichment in Determining Chemical Abundances during the First 600 Myr}},
author = {Annalisa Citro and Yong-Zhong Qian and Claudia M. Scarlata},
journal = {The Astrophysical Journal},
year = {2026},
month = sep,
doi = {10.3847/1538-4357/ae9cb0},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae9cb0},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - On the Importance of the Intergalactic and Circumgalactic Medium Enrichment in Determining Chemical Abundances during the First 600 Myr
AU - Annalisa Citro
AU - Yong-Zhong Qian
AU - Claudia M. Scarlata
PY - 2026
DA - 2026/09/30
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/ae9cb0
UR - https://iopscience.iop.org/article/10.3847/1538-4357/ae9cb0
AB - JWST observations show that galaxies at z > 8 exhibit a wide range of carbon-to-oxygen (C/O) ratios at fixed metallicity and systematically elevated nitrogen-to-oxygen (N/O) ratios compared to local galaxies. Proposed explanations include finely tuned star formation histories (SFHs), differential or pristine inflows, top- or bottom-heavy initial mass functions (IMFs), or enrichment from Wolf–Rayet stars, supermassive stars (SMSs), or Population III (Pop III) stars. The observed abundances reflect both in situ production tied to the SFHs and earlier pre-enrichment of the intergalactic and circumgalactic medium (IGM/CGM), which supply the gas inflow that fuels star formation. At such early epochs, SFHs are necessarily brief, and sustained star formation requires inflows to dominate over outflows, making the chemical state of the IGM/CGM especially important. We develop a chemical-evolution model that incorporates (1) enrichment of the IGM/CGM by multiple sources and (2) the observed SFHs of high-redshift galaxies. Applying this model to eight galaxies at z > 8, we find that only specific pre-enrichment scenarios reproduce their observed abundance ratios. For example, the low C/O and high N/O ratios measured in GN-z11 and CEERS-1019 require an IGM/CGM enriched by supermassive stars (SMSs) and pre-enriched to an oxygen metallicity of ∼10 ⁻⁵ of the solar value. We also find that the log ( N / O ) versus 12 + log ( O / H ) plane provides more stringent constraints on enrichment pathways than the log ( C / O ) versus 12 + log ( O / H ) plane. Overall, our results highlight the crucial role of IGM/CGM chemical composition in chemical-evolution models at z > 8 and underscore the significant influence of SMSs on early carbon, nitrogen, and oxygen abundances.
SN - 0004-637X
SN - 1538-4357
ER -