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Abstract We present chemical abundance ratios of 70 star-forming galaxies at z ∼ 4–10 observed by the JWST/NIRSpec Early Release Observations, GLASS, and CEERS programs. Among the 70 galaxies, we have pinpointed two galaxies, CEERS₀1019 at z = 8. 68 and GLASS₁50008 at z = 6. 23, with extremely low C/N (C/N ≲ −1), evidenced with C iii ] λλ 1907, 1909, N iii ] λ 1750, and N iv ] λλ 1483, 1486, which show high N/O ratios (N/O ≳ 0. 5) comparable with the one of GN-z11, regardless of whether stellar or active galactic nucleus radiation is assumed. Such low C/N and high N/O ratios found in CEERS₀1019 and GLASS₁50008 (additionally identified in GN-z11) are largely biased toward the equilibrium of the CNO cycle, suggesting that these three galaxies are enriched by metals processed by the CNO cycle. On the C/N versus O/H plane, these three galaxies do not coincide with Galactic H ii regions, normal star-forming galaxies, and nitrogen-loud quasars with asymptotic giant branch stars, but with globular-cluster (GC) stars, indicating a connection with GC formation. We compare the C/O and N/O of these three galaxies with those of theoretical models and find that these three galaxies are explained by scenarios with dominant CNO-cycle materials, i. e. , Wolf–Rayet stars, supermassive (10 3 –10 5 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 four galaxies with very low Ne/O, log (Ne/O) < −1. 0, indicating abundant massive (≳30 M ⊙) stars.
Isobe et al. (Fri,) studied this question.