Caught Napping by JWST UNCOVER+MegaScience: Constraining bursty star formation histories and number densities of mini-quenched galaxies at redshifts 4-7

@misc{khullar2026caught,
  title = {{Caught Napping by JWST UNCOVER+MegaScience: Constraining bursty star formation histories and number densities of mini-quenched galaxies at redshifts 4-7}},
  author = {Gourav Khullar and Rachel Bezanson and Katherine A. Suess and Ikki Mitsuhashi and David J. Setton and Joel Leja and Sedona H. Price and Katherine E. Whitaker and Emilie Burnham and John R. Weaver and Iryna Chemerynska and Lukas J. Furtak and Jenny Greene and Bingjie Wang and Hakim Atek and Gabe Brammer and Olivia R. Cooper and Robert Feldmann and Seiji Fujimoto and Anna de Graaff and Ivo Labbe and Danilo Marchesini and Ian McConachie and Tim B. Miller and Abby Mintz and Themiya Nanayakkara and Pascal Oesch and Richard Pan and Casey Papovich and Yunchong Zhang},
  howpublished = {arXiv},
  year = {2026},
  month = aug,
  doi = {10.48550/arxiv.2608.30011},
  eprint = {2608.30011},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2608.30011},
  note = {CC BY-NC-SA 4.0},
}

TY  - UNPB
TI  - Caught Napping by JWST UNCOVER+MegaScience: Constraining bursty star formation histories and number densities of mini-quenched galaxies at redshifts 4-7
AU  - Gourav Khullar
AU  - Rachel Bezanson
AU  - Katherine A. Suess
AU  - Ikki Mitsuhashi
AU  - David J. Setton
AU  - Joel Leja
AU  - Sedona H. Price
AU  - Katherine E. Whitaker
AU  - Emilie Burnham
AU  - John R. Weaver
AU  - Iryna Chemerynska
AU  - Lukas J. Furtak
AU  - Jenny Greene
AU  - Bingjie Wang
AU  - Hakim Atek
AU  - Gabe Brammer
AU  - Olivia R. Cooper
AU  - Robert Feldmann
AU  - Seiji Fujimoto
AU  - Anna de Graaff
AU  - Ivo Labbe
AU  - Danilo Marchesini
AU  - Ian McConachie
AU  - Tim B. Miller
AU  - Abby Mintz
AU  - Themiya Nanayakkara
AU  - Pascal Oesch
AU  - Richard Pan
AU  - Casey Papovich
AU  - Yunchong Zhang
PY  - 2026
DA  - 2026/08/30
PB  - arXiv
DO  - 10.48550/arxiv.2608.30011
UR  - https://arxiv.org/abs/2608.30011
AB  - We explore the prevalence of mini-quenched or ``napping'' galaxies selected from spectroscopic and photometric samples in the UNCOVER/MegaScience survey. These galaxies are empirically identified by the presence of moderate Balmer breaks, weak emission lines (EW(Hα) < 100A) and relatively blue UV continua. We infer the star formation histories (SFHs) of our sample using flexible non-parametric models with Prospector optimized to capture recent episodes of bursty star formation and quenching, and find that they are uniquely identifiable in the SFR_10/SFR_100 parameter space moving towards (temporary) quiescence. We demonstrate that although spectroscopy is best able to identify rapidly declining SFRs, densely sampled medium-band photometry recover these key spectral features and thus robustly identify pure samples of this transient phase -- with imaging alone. We quantify the number density of napping galaxies at z=4−7 in the Abell 2744 lensing field, finding 8 spectroscopically confirmed nappers and 60 photometric candidates spanning log_10(M_*/M_⊙) = 7.5−10. We verify that the photometry alone can identify a pure sample of nappers, leveraging a smaller high signal-to-noise ratio spectroscopic sample. Consistent with previous studies, we find that nappers are most common at low stellar mass (log_10(M_*/M_⊙) ∼9). We see a hint that the number densities increase from z∼6 to z∼4, though our small sample is likely affected by cosmic variance. Our study demonstrates the increasing importance of stochastic star formation as a regulator of low-mass galaxy growth in the several hundred Myr after reionization, and offers a direct observational testbed for the strength and duty cycle of stellar feedback in cosmological simulations.
ER  -