Caught Napping by JWST UNCOVER+MegaScience: Constraining bursty star formation histories and number densities of mini-quenched galaxies at redshifts 4-7
Year: 2026
Type: preprint
Abstract: 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 ($EW(Hα) < 100$A) 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$_\odot$) $= 7.5-10$. 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$_\odot$) $\sim9$). We see a hint that the number densities increase from $z\sim6$ to $z\sim4$, 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.
Source: arXiv (Cornell University)
Authors: Khullar, Gourav, Bezanson, Rachel, Suess, Katherine A., Mitsuhashi, Ikki, Setton, David J., Leja, Joel, Price, Sedona H., Whitaker, Katherine E., Burnham, Emilie, Weaver, John R., Chemerynska, Iryna, Furtak, Lukas J., Greene, Jenny, Wang, Bingjie, Atek, Hakim, Brammer, Gabe, Cooper, Olivia R., Feldmann, Robert, Fujimoto, Seiji, de Graaff, Anna, Labbe, Ivo, Marchesini, Danilo, McConachie, Ian, Miller, Tim B., Mintz, Abby, Nanayakkara, Themiya, Oesch, Pascal, Pan, Richard, Papovich, Casey, Zhang, Yunchong
Institutions: University of Pittsburgh, University of California, Santa Cruz, University of Colorado Boulder, Princeton University, Space Telescope Science Institute, University of Copenhagen, University of Massachusetts Amherst, Centre National de la Recherche Scientifique, Institut d'Astrophysique de Paris, Sorbonne Université, The University of Texas at Austin, University of Zurich, University of Toronto, Max Planck Institute for Astronomy, Center for Astrophysics Harvard & Smithsonian, Swinburne University of Technology, Tufts University, University of Wisconsin–Madison, The University of Sydney, University of Geneva, Texas A&M University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, National Aeronautics and Space Administration, Brinson Foundation, Research Corporation for Science Advancement, Washington Research Foundation, University of Washington, Research Corporation for Scientific Advancement, Space Telescope Science Institute, National Radio Astronomy Observatory, European Commission, Danmarks Grundforskningsfond, Max-Planck-Gesellschaft, Smithsonian Astrophysical Observatory, Center for Research Computing, University of Pittsburgh, Institute for Data Intensive Research in Astrophysics and Cosmology, University of Washington
Awards: G103270039, G1108340105, G145748691, G256731684, G2592393619, G3384453195, Cosmic Dawn Center (DAWN), G433322167, G4518818167, G4693797371, G5568641063, MRI: Acquisition of Cutting-Edge GPU and MPI Nodes for the Interdisciplinary Pitt Center for Research Computing, G58316358, G6273510985, G6379244761, G6462785651, Postdoctoral Fellowship: AAPF: Resolving the interstellar conditions and cosmic consequences of highly efficient star formation
OpenAlex ID: W7204933189