The KLEVER survey: Nitrogen abundances at z ∼ 2 and probing the existence of a fundamental nitrogen relation

We present a comparison of the nitrogen-to-oxygen ratio (N/O) in 37high-redshift galaxies at $z\sim$2 taken from the KMOS Lensed Emission Linesand VElocity Review (KLEVER) Survey with a comparison sample of local galaxies,taken from the Sloan Digital Sky Survey (SDSS). The KLEVER sample shows only amild enrichment in N/O of $+$0.1 dex when compared to local galaxies at a givengas-phase metallicity (O/H), but shows a depletion in N/O of $-$0.36 dex whencompared at a fixed stellar mass (M$_*$). We find a strong anti-correlation inlocal galaxies between N/O and SFR in the M$_*$-N/O plane, similar to theanti-correlation between O/H and SFR found in the mass-metallicity relation(MZR). We use this anti-correlation to construct a fundamental nitrogenrelation (FNR), analogous to the fundamental metallicity relation (FMR). Wefind that KLEVER galaxies are consistent with both the FMR and the FNR. Thissuggests that the depletion of N/O in high-$z$ galaxies when considered at afixed M$_*$ is driven by the redshift-evolution of the mass-metallicityrelation in combination with a near redshift-invariant N/O-O/H relation.Furthermore, the existence of an fundamental nitrogen relation suggests thatthe mechanisms governing the fundamental metallicity relation must be probed bynot only O/H, but also N/O, suggesting pure-pristine gas inflows are not theprimary driver of the FMR, and other properties such as variations in galaxyage and star formation efficiency must be important.