James Webb Space Telescope Feed Post

CEERS_01019 and GLASS_150008: JWST Identification of Extremely Low C/N Galaxies with [N/O]>=0.5 at z~6-10 Evidencing the Early CNO-Cycle Enrichment and a Connection with Globular Cluster Formation

Emission line detections of GLASS 150008 and CEERS 01019. (Left) 2'' × 2'' JWST/NIRCam image with blue/green/red corresponding to F150W/F277W/F444W. (Right) Smoothed 1D and 2D spectra around N iv], O iii], N iii], and C iii] shown by the black solid lines and the color maps, respectively. The emission lines are highlighted in yellow, while the highlights for the undetected emission lines are omitted. Restframe wavelengths of the emission lines are shown by the vertical black dotted lines. The horizontal gray lines denote the continuum level. The horizontal white lines on the 2D spectra indicate the extraction aperture for the 1D spectra. Abstract: We present chemical abundance ratios of 70 star-forming galaxies at z~4-10 observed by the JWST/NIRSpec ERO, GLASS, and CEERS programs. Among the 70 galaxies, we have pinpointed 2 galaxies, CEERS_01019 at z=8.68 and GLASS_150008 at z=6.23, with extremely low C/N ([C/N]?-1), evidenced with CIII]??1907,1909, NIII]?1750, and NIV]??1483,1486, which show high N/O ratios ([N/O]?0.5) comparable with the one of GN-z11 regardless of whether stellar or AGN radiation is assumed. Such low C/N and high N/O ratios found in CEERS_01019 and GLASS_150008 (additionally identified in GN-z11) are largely biased towards the equilibrium of the CNO cycle, suggesting that these 3 galaxies are enriched by metals processed by the CNO cycle. On the C/N vs. O/H plane, these 3 galaxies do not coincide with Galactic HII regions, normal star-forming galaxies, and nitrogen-loud quasars with asymptotic giant branch stars, but globular-cluster (GC) stars, indicating a connection with GC formation. We compare C/O and N/O of these 3 galaxies with those of theoretical models, and find that these 3 galaxies are explained by scenarios with dominant CNO-cycle materials, i.e. Wolf-Rayet stars, supermassive (103-105 M?) stars, and tidal disruption events, interestingly with a requirement of frequent direct collapses. For all the 70 galaxies, we present measurements of Ne/O, S/O, and Ar/O, together with C/O and N/O. We identify 4 galaxies with very low Ne/O, log(Ne/O)<-1.0, indicating abundant massive (?30 M?) stars.