James Webb Space Telescope Feed Post

Early Results from GLASS-JWST. XXI: Rapid assembly of a galaxy at z=6.23 revealed by its C/O abundance Published: 1/17/2023 9:00:05 PM Updated: 5/21/2023 8:31:39 AM

Paper 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 \log{\mathrm{(C/O)}} = -1.01\pm0.12 (stat) \pm0.15 (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 million years 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\,\mathrm{M}_* / \mathrm{M_{sun}} = 8.4^{+0.4}_{-0.2} and specific star formation rate sSFR ~eq 20 Gyr^{-1}. These results showcase the value of chemical abundances and C/O in particular to study the earliest stages of galaxy assembly.