Early Results from GLASS–JWST. XXI. Rapid Asembly of a Galaxy at z = 6.23 Revealed by Its C/O Abundance

• Published in: Astrophysical journal. Letters 2023-07, Vol.951 (1), p.L17
• Main Authors: Jones, Tucker, Sanders, Ryan, Chen, Yuguang, Wang, Xin, Morishita, Takahiro, Roberts-Borsani, Guido, Treu, Tommaso, Dressler, Alan, Merlin, Emiliano, Paris, Diego, Santini, Paola, Bergamini, Pietro, Henry, A., Huntzinger, Erin, Nanayakkara, Themiya, Boyett, Kristan, Bradac, Marusa, Brammer, Gabriel, Calabró, Antonello, Glazebrook, Karl, Grasha, Kathryn, Mascia, Sara, Pentericci, Laura, Trenti, Michele, Vulcani, Benedetta
• Format: Article
• Language: English
• Subjects: Abundance; Abundance ratios; Big bang cosmology; Carbon; Chemical analysis; Emission line galaxies; Emission lines; Galaxies; Galaxy abundances; High-redshift galaxies; Nuclear fusion; Oxygen; Spectral energy distribution; Star & galaxy formation; Star formation; Star formation rate; Stars; Stellar mass; Supernovae
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/acd938

The abundance of carbon relative to oxygen (C/O) is a promising probe of star formation history in the early universe, as the ratio changes with time due to production of these elements by different nucleosynthesis pathways. We present a measurement of log ( C / O ) = − 1.01 ± 0.12 (stat) ±0.15 (sys) in a z = 6.23 galaxy observed as part of the GLASS–JWST Early Release Science Program. Notably, we achieve good precision thanks to the detection of the rest-frame ultraviolet O iii ], C iii ], and C iv emission lines delivered by JWST/NIRSpec. The C/O abundance is ∼0.8 dex lower than the solar value and is consistent with the expected yield from core-collapse supernovae, indicating that longer-lived intermediate-mass stars have not fully contributed to carbon enrichment. This in turn implies rapid buildup of a young stellar population with age ≲100 Myr in a galaxy seen ∼900 Myr after the big bang. Our chemical abundance analysis is consistent with spectral energy distribution modeling of JWST/NIRCam photometric data, which indicates a current stellar mass log M * / M ☉ = 8.4 − 0.2 + 0.4 and specific star formation rate ≃20 Gyr −1 . These results showcase the value of chemical abundances and C/O in particular to study the earliest stages of galaxy assembly.