OASIS I: Spectroscopy of Mini-Quenched and Lulling Galaxies Constrains the Quiet Side of Bursty Star Formation at z > 4
Abstract
JWST has revealed that star formation in early galaxies is bursty, including episodes of violent suppression, so-called mini-quenching. But these were largely serendipitous discoveries in samples of UV-bright, emission-line-dominated galaxies, so that the quiet side of the burst cycle has remained poorly explored. With the JWST Cycle 3 program OASIS (GO 5997), we searched for such galaxies deliberately, using deep 28-hour NIRSpec/PRISM spectroscopy across the full burst cycle at z>4. We identify three mini-quenched galaxies with log(M*/Msun) = 8.3-8.9 and no detectable Balmer emission, at least 1.2-1.7 dex below the star-forming main sequence (SFMS), five lulling galaxies with weak Balmer emission above the quenching threshold, and 17 nearly-main-sequence galaxies just below the SFMS. Finding them required spectroscopy: seven of our ten photometric candidates for suppressed (mini-quenched and lulling) galaxies turned out to be nearly-MS or above the SFMS, and photometric fits overestimate their current star-formation rates and cannot distinguish lulling from mini-quenched ones. The suppressed galaxies are common: five of the eight come from tiers not selected on star-formation state, where they make up 29% of the galaxies at z = 4-5.5 and log(M*/Msun) = 8-9.5, a number density of ~1.6x10^-3 Mpc^-3 dex^-1. Simulations predict them to be an order of magnitude rarer at these masses and to occur mainly at lower masses. The suppressed galaxies are also old: Balmer-break strength and stellar age both increase as galaxies fall further below the SFMS, with light-weighted ages of 5 Myr for galaxies above it, ~30 Myr for the lulling galaxies and above 100 Myr for the mini-quenched ones. They show little stellar reddening (E(B-V) < 0.2), consistent with depleted gas reservoirs. Suppressed phases at z>4 are therefore neither rare nor brief, but a common and lasting part of early galaxy growth.
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BibTeX
@misc{looser2026oasis,
title = {{OASIS I: Spectroscopy of Mini-Quenched and Lulling Galaxies Constrains the Quiet Side of Bursty Star Formation at z > 4}},
author = {Tobias J. Looser and Francesco D'Eugenio and William M. Baker and Santiago Arribas and Andrew J. Bunker and Stefano Carniani and Stéphane Charlot and Jacopo Chevallard and Mirko Curti and Qiao Duan and Kevin Hainline and Jakob M. Helton and Yuki Isobe and Benjamin D. Johnson and Pierluigi Rinaldi and Brant Robertson and Fengwu Sun and Sandro Tacchella and James A. A. Trussler and Hannah Übler and Joris Witstok and Zihao Wu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.41489},
eprint = {2610.41489},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.41489},
}
RIS
TY - UNPB
TI - OASIS I: Spectroscopy of Mini-Quenched and Lulling Galaxies Constrains the Quiet Side of Bursty Star Formation at z > 4
AU - Tobias J. Looser
AU - Francesco D'Eugenio
AU - William M. Baker
AU - Santiago Arribas
AU - Andrew J. Bunker
AU - Stefano Carniani
AU - Stéphane Charlot
AU - Jacopo Chevallard
AU - Mirko Curti
AU - Qiao Duan
AU - Kevin Hainline
AU - Jakob M. Helton
AU - Yuki Isobe
AU - Benjamin D. Johnson
AU - Pierluigi Rinaldi
AU - Brant Robertson
AU - Fengwu Sun
AU - Sandro Tacchella
AU - James A. A. Trussler
AU - Hannah Übler
AU - Joris Witstok
AU - Zihao Wu
PY - 2026
DA - 2026/10/30
PB - arXiv
DO - 10.48550/arxiv.2610.41489
UR - https://arxiv.org/abs/2610.41489
AB - JWST has revealed that star formation in early galaxies is bursty, including episodes of violent suppression, so-called mini-quenching. But these were largely serendipitous discoveries in samples of UV-bright, emission-line-dominated galaxies, so that the quiet side of the burst cycle has remained poorly explored. With the JWST Cycle 3 program OASIS (GO 5997), we searched for such galaxies deliberately, using deep 28-hour NIRSpec/PRISM spectroscopy across the full burst cycle at z>4. We identify three mini-quenched galaxies with log(M*/Msun) = 8.3-8.9 and no detectable Balmer emission, at least 1.2-1.7 dex below the star-forming main sequence (SFMS), five lulling galaxies with weak Balmer emission above the quenching threshold, and 17 nearly-main-sequence galaxies just below the SFMS. Finding them required spectroscopy: seven of our ten photometric candidates for suppressed (mini-quenched and lulling) galaxies turned out to be nearly-MS or above the SFMS, and photometric fits overestimate their current star-formation rates and cannot distinguish lulling from mini-quenched ones. The suppressed galaxies are common: five of the eight come from tiers not selected on star-formation state, where they make up 29% of the galaxies at z = 4-5.5 and log(M*/Msun) = 8-9.5, a number density of ~1.6x10^-3 Mpc^-3 dex^-1. Simulations predict them to be an order of magnitude rarer at these masses and to occur mainly at lower masses. The suppressed galaxies are also old: Balmer-break strength and stellar age both increase as galaxies fall further below the SFMS, with light-weighted ages of 5 Myr for galaxies above it, ~30 Myr for the lulling galaxies and above 100 Myr for the mini-quenched ones. They show little stellar reddening (E(B-V) < 0.2), consistent with depleted gas reservoirs. Suppressed phases at z>4 are therefore neither rare nor brief, but a common and lasting part of early galaxy growth.
ER -