Abstract Extreme nitrogen enhancement relative to oxygen, recently found in very high-redshift galaxies, has been seen in local star-forming galaxies displaying high log(N/O) values (≥−1.1) at relatively low O abundances, 12+log(O/H) ≤ 8. Understanding the physical origins of these extreme N-emitters at low redshifts enables us to better constrain chemical enrichment mechanisms that drove such high log(N/O) values in the early Universe. With direct N and O abundances derived for 944 SFGs with spectroscopic observational data from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1), we report the discovery of 19 extreme N-emitters at low-z (z0.5). Our sample of N-emitters represents a five-fold increase in their known number at low-z with 12+log(O/H) ≤ 8, and statistically, 2.21 ± 0.91 per cent of DESI DR1 SFGs with reliable O and N abundances obtained directly, are extreme N-emitters. The sample spans a mass range of ~107–1010 M⊙ with 12+log(O/H) range of ~7.1–8.2, and the N-emitter fraction is found to increase with increasing stellar mass and decreasing metallicity. The most extreme N-emitter in our sample has log(N/O)=−0.53 ± 0.13, while also having the lowest 12+log(O/H)=7.08 ± 0.09 and the highest stellar mass, log(M*/M⊙)=9.95 ± 0.13 among our sample. With galactic chemical evolution models, we show that sustained N-enhancement by asymptotic giant branch stars, in conjunction with presence of outflows during the evolution of the galaxy, can well explain the high log(N/O) of low-z extreme N-emitters. While single starbursts with outflow are sufficient to explain lower-mass N-emitters, more massive ones require a dual starburst scenario where a secondary starburst is triggered by inflow of gas.
Bhattacharya et al. (Thu,) studied this question.