Galaxy formation and evolution

Abstract:

Abstract We present nitrogen abundance measurements based on the low-ionisation [N ii] λ6583 emission line for 588 galaxies between 1.5 < z < 7.0 from the JWST Advanced Deep Extragalactic Survey (JADES). We detect the temperature-sensitive [O iii] λ4363 auroral line in 40 galaxies in our sample, affording Te-based abundances for this subset. We find that the average N/O abundance ratio in this Te −based low-metallicity sample is at least 0.1 dex higher than z ~ 0 samples. In particular, we find significant scatter toward high N/O, with five galaxies being identified with enhanced nitrogen abundances (log (N/O) > −1.1) at low-metallicity (12 + log (O/H) < 8.0) from Te-based measurements. Meanwhile, applying strong-line abundance measurements to the remainder of our sample reveals a further 14 candidate galaxies passing these abundance cuts, implying that around 13 % of 12 + log (O/H) < 8.0 galaxies at these redshifts are nitrogen-enhanced at this level. We find that N/O abundance in low-metallicity systems correlates with SFR, ΣSFR, and $\Sigma _{M_*}$at high redshift, while only in high-metallicity systems does a correlation with M* emerge. Despite healthy representation of these ‘moderately nitrogen-enhanced’ galaxies (−1.1 < log (N/O) ≤ −0.6), no galaxies in our low-metallicity [N ii]-based sample are identified as having log (N/O) > −0.6, abundances that are typical of high-redshift N iii]- and N iv]-emitters. This demonstrates that the extreme nitrogen enhancements seen in some N iii]- and N iv]-emitters are only attained during the most extreme starbursts. This suggests that these elevated abundances are caused by enrichment from young massive stars in extreme environments and that the impact of this enrichment pathway is milder, though still important, for high-redshift systems on the star-forming main sequence.