Balmer Break Measurements Trace Departures from the Star-Forming Main Sequence at 1<z<4 with JWST/NIRSpec
Abstract
We present JWST/NIRSpec PRISM observations of galaxies at 1<z<4 to study the relation between Balmer-break strength (DBalmer) and recent star formation. Using NIRSpec spectra from the JADES Transient Survey in GOODS-S, we measure DBalmer and hydrogen recombination-line equivalent widths, and infer galaxy properties through spectral energy distribution (SED) fitting of the accompanying photometry. We find a clear anti-correlation between DBalmer and the rest-frame equivalent width of Hα+[\ion{N}{2}], such that galaxies with stronger breaks show weaker nebular emission and lower recent star formation activity. DBalmer also correlates with mass-weighted stellar age, supporting its use as an empirical tracer of evolved stellar populations at these redshifts. Star formation rates inferred from Hα, Paγ, and SED fitting are broadly consistent, with scatter likely driven in part by dust attenuation, line-measurement uncertainties, and the different timescales probed by each indicator. Galaxies with stronger DBalmer also tend to lie further below the star-forming main sequence at fixed stellar mass, indicating that DBalmer is linked to recent suppression of star formation. In contrast, we find only a weak relation between DBalmer and SED-derived dust attenuation, suggesting that dust is not the main driver of the observed trends. These results show that DBalmer, combined with recombination-line measurements, is a useful empirical diagnostic of galaxies transitioning away from the star-forming population at cosmic noon.
Related
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- The Star-forming Main Sequence and Bursty Star-formation Histories at z > 1.4 in JADES and AURORA
BibTeX
@misc{narisetty2026balmer,
title = {{Balmer Break Measurements Trace Departures from the Star-Forming Main Sequence at $1<z<4$ with JWST/NIRSpec}},
author = {Suprabhas Narisetty and Yongda Zhu and Eiichi Egami and Stefano Carniani and Francesco D'Eugenio and Christa DeCoursey and Christopher N. A. Willmer},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.31827},
eprint = {2609.31827},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.31827},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Balmer Break Measurements Trace Departures from the Star-Forming Main Sequence at 1<z<4 with JWST/NIRSpec
AU - Suprabhas Narisetty
AU - Yongda Zhu
AU - Eiichi Egami
AU - Stefano Carniani
AU - Francesco D'Eugenio
AU - Christa DeCoursey
AU - Christopher N. A. Willmer
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2609.31827
UR - https://arxiv.org/abs/2609.31827
AB - We present JWST/NIRSpec PRISM observations of galaxies at 1<z<4 to study the relation between Balmer-break strength (D_Balmer) and recent star formation. Using NIRSpec spectra from the JADES Transient Survey in GOODS-S, we measure D_Balmer and hydrogen recombination-line equivalent widths, and infer galaxy properties through spectral energy distribution (SED) fitting of the accompanying photometry. We find a clear anti-correlation between D_Balmer and the rest-frame equivalent width of Hα+[\ion{N}{2}], such that galaxies with stronger breaks show weaker nebular emission and lower recent star formation activity. D_Balmer also correlates with mass-weighted stellar age, supporting its use as an empirical tracer of evolved stellar populations at these redshifts. Star formation rates inferred from Hα, Paγ, and SED fitting are broadly consistent, with scatter likely driven in part by dust attenuation, line-measurement uncertainties, and the different timescales probed by each indicator. Galaxies with stronger D_Balmer also tend to lie further below the star-forming main sequence at fixed stellar mass, indicating that D_Balmer is linked to recent suppression of star formation. In contrast, we find only a weak relation between D_Balmer and SED-derived dust attenuation, suggesting that dust is not the main driver of the observed trends. These results show that D_Balmer, combined with recombination-line measurements, is a useful empirical diagnostic of galaxies transitioning away from the star-forming population at cosmic noon.
ER -