Discovery of new N-emitters over a wide redshift range
4 affiliations
- 1Observatoire de Genève, Université de Genève
- 2CNRS, IRAP
- 3Institut d’Astrophysique de Paris, UMR 7095 CNRS, Sorbonne Université
- 4Cosmic Dawn Center (DAWN), Niels Bohr Institute, University of Copenhagen
Abstract
Context. Recent James Webb Space Telescope (JWST) observations have revealed a small number of galaxies with UV spectra exhibiting intense nitrogen emission lines, which are not typically detected in galaxy spectra. The observations indicate super-solar N/O abundances at low metallicity, a phenomenon whose nature is currently intensely debated. Aims. To better understand these enigmatic objects and provide new constraints on proposed scenarios, we did a systematic search for galaxies with UV nitrogen emission lines (N IV ] λ 1486 and/or N III ] λ 1750). Methods. Using public JWST NIRSpec data, we identified 45 N-emitters with robust N III ] or N IV ] detections, including four previously known objects. We then classified these objects, determined relative C, N, O, and H chemical abundance ratios, determined other properties, and carried out a statistical analysis of the N-emitter population. Results. We find N-emitters at redshifts z ∼ 3 − 11 spanning a broad diversity of galaxies in terms of morphology, UV magnitude, stellar mass, star formation rate, metallicity, and rest-optical emission line strengths. The UV nitrogen lines show typical equivalent widths (EW) between ∼5 Å and up to ∼100 Å in a few cases. Diverse ionisation conditions, as traced by N IV ] λ 1486/N III ] λ 1750, are observed. The carbon lines (C IV λ 1550 and C III ] λ 1909) are generally fainter than the N lines. Using strong line calibrations established at high-redshift, we find metallicities 12 + log(O/H)∼7.15 − 8.5, spanning up to high metallicity values. The H β EW of N-emitters varies strongly, and sources with low EWs show clear signs of a Balmer break, indicative of composite stellar populations combining both young (≲10 Myr) stars responsible for the UV emission lines and an older population contributing to the rest-optical spectrum. Super-solar N/O ratios are found in all N-emitters. C/O abundances are comparable to those of galaxies at the same metallicity, and all N-emitters show either high N/C ratios or lower limits (log(N/C) ≳ 0.5), regardless of metallicity. The observed abundance ratios are compatible with ejecta from H-burning and show no signs of carbon enhancements, even at higher metallicities. Finally, we find that the fraction of N-emitters increases with redshift, and we quantify this evolution. Conclusions. Our study increases the sample of known N-emitters by a factor of ∼3, reveals a diversity of properties among N-emitters, and provides new constraints on their nature.
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BibTeX
@article{morel2026discovery,
title = {{Discovery of new N-emitters over a wide redshift range}},
author = {I. Morel and D. Schaerer and R. Marques-Chaves and Nikos Prantzos and Corinne Charbonnel and G. Brammer and Mengyuan Xiao and Miroslava Dessauges-Zavadsky},
journal = {Astronomy and Astrophysics},
year = {2026},
month = may,
doi = {10.1051/0004-6361/202558256},
url = {https://doi.org/10.1051/0004-6361/202558256},
note = {CC BY},
}
RIS
TY - JOUR
TI - Discovery of new N-emitters over a wide redshift range
AU - I. Morel
AU - D. Schaerer
AU - R. Marques-Chaves
AU - Nikos Prantzos
AU - Corinne Charbonnel
AU - G. Brammer
AU - Mengyuan Xiao
AU - Miroslava Dessauges-Zavadsky
PY - 2026
DA - 2026/05/12
JO - Astronomy and Astrophysics
DO - 10.1051/0004-6361/202558256
UR - https://doi.org/10.1051/0004-6361/202558256
AB - Context. Recent James Webb Space Telescope (JWST) observations have revealed a small number of galaxies with UV spectra exhibiting intense nitrogen emission lines, which are not typically detected in galaxy spectra. The observations indicate super-solar N/O abundances at low metallicity, a phenomenon whose nature is currently intensely debated. Aims. To better understand these enigmatic objects and provide new constraints on proposed scenarios, we did a systematic search for galaxies with UV nitrogen emission lines (N IV ] λ 1486 and/or N III ] λ 1750). Methods. Using public JWST NIRSpec data, we identified 45 N-emitters with robust N III ] or N IV ] detections, including four previously known objects. We then classified these objects, determined relative C, N, O, and H chemical abundance ratios, determined other properties, and carried out a statistical analysis of the N-emitter population. Results. We find N-emitters at redshifts z ∼ 3 − 11 spanning a broad diversity of galaxies in terms of morphology, UV magnitude, stellar mass, star formation rate, metallicity, and rest-optical emission line strengths. The UV nitrogen lines show typical equivalent widths (EW) between ∼5 Å and up to ∼100 Å in a few cases. Diverse ionisation conditions, as traced by N IV ] λ 1486/N III ] λ 1750, are observed. The carbon lines (C IV λ 1550 and C III ] λ 1909) are generally fainter than the N lines. Using strong line calibrations established at high-redshift, we find metallicities 12 + log(O/H)∼7.15 − 8.5, spanning up to high metallicity values. The H β EW of N-emitters varies strongly, and sources with low EWs show clear signs of a Balmer break, indicative of composite stellar populations combining both young (≲10 Myr) stars responsible for the UV emission lines and an older population contributing to the rest-optical spectrum. Super-solar N/O ratios are found in all N-emitters. C/O abundances are comparable to those of galaxies at the same metallicity, and all N-emitters show either high N/C ratios or lower limits (log(N/C) ≳ 0.5), regardless of metallicity. The observed abundance ratios are compatible with ejecta from H-burning and show no signs of carbon enhancements, even at higher metallicities. Finally, we find that the fraction of N-emitters increases with redshift, and we quantify this evolution. Conclusions. Our study increases the sample of known N-emitters by a factor of ∼3, reveals a diversity of properties among N-emitters, and provides new constraints on their nature.
SN - 0004-6361
SN - 1432-0746
ER -