Year: 2026
Type: article
Abstract: JWST has revealed a population of “dormant” galaxies at z > 5 that have recently halted their star formation and are characterized by weak emission lines and significant Balmer breaks. Until now, only four such galaxies have been reported at z > 5, three with low stellar masses, M* < 109 M⊙ (so-called mini-quenched galaxies), and one massive quiescent galaxy with M* = 1010.2 M⊙; no such galaxy had been reported at intermediate masses. Here, we present a systematic search for dormant galaxies at 5 < z < 7.4 that halted star formation at least 10 Myr before the time of observation. To do this, we made use of all the publicly available NIRSpec prism data in the DAWN JWST Archive (DJA) and select galaxies with low Hα equivalent widths (EW0 < 50 Å) and strong Balmer breaks (Fν, 4200/Fν, 3500 > 1.4). We find 14 dormant galaxies with stellar masses ranging from 107.6 − 1010.5, revealing an intermediate-mass population. By construction, these 14 sources are located about 1 dex below the star-forming main sequence. Their star formation histories suggest that they halted star formation between 10 and 25 Myr before the time of observation which, according to models, is comparable with the timescales of internally regulated bursts driving a “breathing” mode of star formation. Our results show that ∼1% of the galaxies in the DJA are in a dormant phase of their star formation histories, and they span a wide stellar mass range. These galaxies can be empirically selected using only their spectral features in NIRSpec prism data.
Authors: Alba Covelo-Paz, Corentin Meuwly, Pascal A. Oesch, Callum Witten, Andrea Weibel, Cristian Carvajal-Bohorquez, Laure Ciesla, Emma Giovinazzo, Gabriel Brammer
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, Space Telescope Science Institute, National Research Foundation, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Danmarks Grundforskningsfond, Staatssekretariat für Bildung, Forschung und Innovation
OpenAlex ID: W7114770282
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