Sleeping or Dead? Probing the Quenching Mechanism of JWST Dormant Galaxies at z > 3 with ALMA

@misc{xiao2026sleeping,
  title = {{Sleeping or Dead? Probing the Quenching Mechanism of JWST Dormant Galaxies at z > 3 with ALMA}},
  author = {Mengyuan Xiao and Songnan Qi and Pascal A. Oesch and Longji Bing and Miroslava Dessauges-Zavadsky and Andreas L. Faisst and Mahsa Sanati and Rashmi Gottumukkala and Gabriel Brammer and David Elbaz and Robert Feldmann and Yoshinobu Fudamoto and Lucas C. Kimmig and Benjamin Magnelli and Rui Marques-Chaves and Anurag Amol Sawarkar and Sune Toft and Francesco Valentino and Christina C. Williams},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.19926},
  eprint = {2610.19926},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.19926},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Sleeping or Dead? Probing the Quenching Mechanism of JWST Dormant Galaxies at z > 3 with ALMA
AU  - Mengyuan Xiao
AU  - Songnan Qi
AU  - Pascal A. Oesch
AU  - Longji Bing
AU  - Miroslava Dessauges-Zavadsky
AU  - Andreas L. Faisst
AU  - Mahsa Sanati
AU  - Rashmi Gottumukkala
AU  - Gabriel Brammer
AU  - David Elbaz
AU  - Robert Feldmann
AU  - Yoshinobu Fudamoto
AU  - Lucas C. Kimmig
AU  - Benjamin Magnelli
AU  - Rui Marques-Chaves
AU  - Anurag Amol Sawarkar
AU  - Sune Toft
AU  - Francesco Valentino
AU  - Christina C. Williams
PY  - 2026
DA  - 2026/10/14
PB  - arXiv
DO  - 10.48550/arxiv.2610.19926
UR  - https://arxiv.org/abs/2610.19926
AB  - JWST has revealed a population of "dormant'' galaxies at z>3 with strong Balmer breaks and weak emission lines, whose star formation appears to have declined only recently. Whether these galaxies are undergoing a lasting transition toward quiescence or merely experiencing a temporary suppression of star formation remains unclear. We investigate their molecular gas content using archival ALMA observations of [CII]158um and CO rotational transitions. Starting from all publicly available JWST/NIRSpec prism observations and using joint spectrophotometric fitting, we construct a parent sample at z>3 and log(Mstar/Msun)>9.5 in the ALMA-accessible COSMOS, UDS, and GOODS-South fields. Our final sample comprises 7 dormant galaxies and 15 quiescent galaxies with ALMA constraints on their molecular gas content (mostly 3 sigma upper limits). We find that dormant galaxies exhibit systematically lower star formation rates averaged over the past 10Myr (SFR10Myr) than over the past 100Myr (SFR100Myr), supporting a recent rapid decline in their star formation. For the ~70% of the sample with sufficiently constraining ALMA observations, their molecular gas fractions lie at least ~0.3-2dex below those expected for main-sequence galaxies. Moreover, the molecular gas fractions of dormant galaxies show no systematic difference from those of quiescent galaxies in our sample. This indicates that dormant galaxies have already reached a gas-poor state shortly after quenching and favors a scenario in which the rapid shutdown of star formation is associated with depletion or removal of the molecular gas reservoir, rather than primarily with suppressed star formation efficiency while retaining a substantial molecular gas reservoir. Our results suggest that, if no substantial gas replenishment occurs in the future, dormant galaxies are more consistent with becoming "dead'' than with being temporarily "sleeping''.
ER  -