OASIS II: The Ionized Gas Traces Feedback-Driven Declines into the Quiet Side of Bursty Star Formation at z > 4

@misc{looser2026oasis,
  title = {{OASIS II: The Ionized Gas Traces Feedback-Driven Declines into 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.2610.41490},
  eprint = {2610.41490},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.41490},
}

TY  - UNPB
TI  - OASIS II: The Ionized Gas Traces Feedback-Driven Declines into 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.2610.41490
UR  - https://arxiv.org/abs/2610.41490
AB  - Models of bursty star formation in low-mass (10^8-10^9.5 Msun) galaxies at z>4 differ most in the suppressed phases: what drives the decline, how fast star formation falls, and how long it stays low. OASIS Paper I showed that such quiet galaxies are common and old; here we measure how they got there and how their ionized gas responds. We compare Balmer-line star-formation rates (SFRs) with 100-Myr averages from the stellar continuum, in NIRSpec/PRISM spectra of 54 OASIS galaxies at z>4, including three mini-quenched galaxies below the quenching threshold and five lulling galaxies at least 0.6 dex below the star-forming main sequence (SFMS) but still star-forming. Galaxies above the SFMS rise and fade equally often, whereas those below it are mostly fading: the lulling galaxies formed little more than a tenth of their mass in the last 100 Myr, and their decline began tens to ~100 Myr before observation. Suppressed phases thus last of order 100 Myr, as long as or longer than in most simulations, whereas recovery is much faster: few galaxies below the SFMS are rising. The ionized gas tracks these changes in star formation. [OIII]/[OII] falls from galaxies above the SFMS to the lulling ones, even at fixed mass and after dust correction, and follows the recent change in SFR (SFR_10/SFR_100) more closely than the position relative to the SFMS: two rising galaxies below the SFMS are highly ionized. This is expected if fewer and softer ionizing photons than in strongly star-forming galaxies meet gas depleted by earlier star formation. Lulling galaxies show ISM conditions distinct from those of strongly star-forming galaxies. The declines are faster than passive gas exhaustion predicts, favoring feedback that expels the gas or keeps it from forming stars. Quiet phases are thus long, feedback-driven episodes, and the ionized gas traces where a galaxy is in its burst cycle.
ER  -