Early Results from GLASS-JWST. XXI. Rapid Asembly of a Galaxy at z = 6.23 Revealed by Its C/O Abundance
Santini, Paola; Pentericci, Laura; Treu, Tommaso; Glazebrook, Karl; Nanayakkara, Themiya; Brammer, Gabriel; Dressler, Alan; Boyett, Kristan; Trenti, Michele; Vulcani, Benedetta; Wang, Xin; Grasha, Kathryn; Jones, Tucker; Morishita, Takahiro; Sanders, Ryan; Henry, A.; Mascia, Sara; Merlin, Emiliano; Paris, Diego; Roberts-Borsani, Guido; Bradac, Marusa; Bergamini, Pietro; Chen, Yuguang; Huntzinger, Erin; Calabró, Antonello
United States, China, Italy, Australia, Slovenia, Denmark
Abstract
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 $\mathrm{log}({\rm{C}}/{\rm{O}})=-1.01\pm 0.12$ (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 $\mathrm{log}\,{M}_{* }/{M}_{\odot }={8.4}_{-0.2}^{+0.4}$ 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.