Abstract
ABSTRACT We present measurements of the electron-temperature-based oxygen abundance for a highly star-forming galaxy at z = 3.08, COSMOS-1908. This is the highest redshift at which [O iii]λ4363 has been detected and the first time that this line has been measured at z > 2 . We estimate an oxygen abundance of 12 + log ( O / H ) = 8.00 − 0.14 + 0.13 . This galaxy is a low-mass ( 10 9.3 M ⊙ ), highly star-forming (∼50 M ⊙ yr−1) system that hosts a young stellar population (∼160 Myr). We investigate the physical conditions of the ionized gas in COSMOS-1908 and find that this galaxy has a high ionization parameter, little nebular reddening ( E ( B − V ) gas < 0.14 ), and a high electron density ( n e ∼ 500 cm−3). We compare the ratios of strong oxygen, neon, and hydrogen lines to the direct-method oxygen abundance for COSMOS-1908 and additional star-forming galaxies at z = 0 − 1.8 with [O iii]λ4363 measurements and show that galaxies at z ∼ 1 – 3 follow the same strong-line correlations as galaxies in the local universe. This agreement suggests that the relationship between ionization parameter and O/H is similar for z ∼ 0 and high-redshift galaxies. These results imply that metallicity calibrations based on lines of oxygen, neon, and hydrogen do not strongly evolve with redshift and can reliably estimate abundances out to z ∼ 3 , paving the way for robust measurements of the evolution of the mass–metallicity relation to high redshift.
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