Nitrogen abundances in star-forming galaxies 2.2 Gyr after the Big Bang are not elevated

Using deep, medium-resolution, JWST rest-optical spectra of a sample of typical star-forming galaxies (Lyman-break galaxies and Lyman-α emitters) from the LyC22 survey at z ∼ 3, we determined the nebular abundances of N, O, and Ne relative to H for a subsample of 25 objects with a direct method based on auroral [O III] λ4363 line detections. Our measurements increased the number of accurate N/O determinations at z ∼ 2 − 4 using a homogeneous approach. We found a mean value of log(N/O) = −+0.25−0.21 over a metallicity range of 12 + log(O/H) = 7.56 to 8.44. The observed N/O ratio and scatter are indistinguishable from that observed in low-z galaxies and H II regions over the same metallicity range, thus showing no redshift evolution of N/O for typical galaxies over a significant fraction of cosmic time. We also show that typical z ∼ 3 galaxies have a similar offset in the BPT diagram to galaxies from the low-z Lyman Continuum Survey (LzLCS) when compared to the average of SDSS galaxies, and we demonstrate that this offset is not due to enhanced nitrogen abundances. Our results establish a basis for future studies of the evolution of N and O at higher redshifts.