JWST Spectra Conclusively Show an Excess of Neutral Gas Outflows in Quiescent Galaxies at z=2-5

Abstract

Galaxies exhibit a broad range of star formation activity, from actively star-forming to quiescent systems. Yet, the mechanisms responsible for the rapid shutdown and continued suppression of star formation remain poorly understood, particularly for the quiescent galaxies recently uncovered by JWST at z>3. Neutral gas outflows provide a direct tracer of gas removal and regulation in quiescent galaxies. We therefore present a NaID λλ5891,5897 absorption--line stacking analysis of 274 galaxies at z=2--5 drawn from the DAWN JWST Archive (DJA) and the EMBER JWST program, using JWST/NIRSpec medium-resolution grating spectroscopy and NIRCam photometry. NaID absorption is detected in all quiescent galaxy stacks spanning z=2--5, providing the first statistical evidence that neutral gas outflows are a ubiquitous feature of quiescent galaxies in the early Universe. Compared to the non-quiescent galaxy stacks, the quiescent stacks show mass loading factors higher by 2--4 dex, with mass outflow rates Ṁ_out ∼ 9--30 M_⊙ yr⁻¹ elevated by ∼0.5--$1$ dex and outflow velocities v_out ∼ 310--570 km s⁻¹ higher by a factor of ∼2. The extreme mass loading factor values and declining star formation histories strongly indicate that these outflows cannot be driven by current star formation alone. In the statistically reliable quiescent redshift bins at 2 ≤ z < 3 and 3 ≤ z < 4, the elevated [N II]/Hα and [O III]/Hβ ratios are consistent with a possible AGN contribution, suggesting that non-stellar feedback may play a role in sustaining quiescence in galaxies at these epochs.

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BibTeX RIS

BibTeX

@misc{oh2026jwst,
  title = {{JWST Spectra Conclusively Show an Excess of Neutral Gas Outflows in Quiescent Galaxies at z=2-5}},
  author = {Rion Oh and Gourav Khullar and Arianna S. Long and Julissa Sarmiento and Hollis B. Akins and Caitlin M. Casey and Yingjie Cheng and Andreas L. Faisst and Maximilien Franco and Ghassem Gozaliasl and Micheaela Hirschmann and Erini Lambrides and Jacqueline E. McCleary and Tiara Anderson and David C. Andrews and Dylan Berry and Nguyen Binh and Elaine Gammon},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.09459},
  eprint = {2609.09459},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.09459},
  note = {CC BY-NC-SA 4.0},
}

RIS

TY  - UNPB
TI  - JWST Spectra Conclusively Show an Excess of Neutral Gas Outflows in Quiescent Galaxies at z=2-5
AU  - Rion Oh
AU  - Gourav Khullar
AU  - Arianna S. Long
AU  - Julissa Sarmiento
AU  - Hollis B. Akins
AU  - Caitlin M. Casey
AU  - Yingjie Cheng
AU  - Andreas L. Faisst
AU  - Maximilien Franco
AU  - Ghassem Gozaliasl
AU  - Micheaela Hirschmann
AU  - Erini Lambrides
AU  - Jacqueline E. McCleary
AU  - Tiara Anderson
AU  - David C. Andrews
AU  - Dylan Berry
AU  - Nguyen Binh
AU  - Elaine Gammon
PY  - 2026
DA  - 2026/09/08
PB  - arXiv
DO  - 10.48550/arxiv.2609.09459
UR  - https://arxiv.org/abs/2609.09459
AB  - Galaxies exhibit a broad range of star formation activity, from actively star-forming to quiescent systems. Yet, the mechanisms responsible for the rapid shutdown and continued suppression of star formation remain poorly understood, particularly for the quiescent galaxies recently uncovered by JWST at z>3. Neutral gas outflows provide a direct tracer of gas removal and regulation in quiescent galaxies. We therefore present a NaID λλ5891,5897 absorption--line stacking analysis of 274 galaxies at z=2--5 drawn from the DAWN JWST Archive (DJA) and the EMBER JWST program, using JWST/NIRSpec medium-resolution grating spectroscopy and NIRCam photometry. NaID absorption is detected in all quiescent galaxy stacks spanning z=2--5, providing the first statistical evidence that neutral gas outflows are a ubiquitous feature of quiescent galaxies in the early Universe. Compared to the non-quiescent galaxy stacks, the quiescent stacks show mass loading factors higher by 2--4 dex, with mass outflow rates Ṁ_out ∼ 9--30 M_⊙ yr^−1 elevated by ∼0.5--$1$ dex and outflow velocities v_out ∼ 310--570 km s^−1 higher by a factor of ∼2. The extreme mass loading factor values and declining star formation histories strongly indicate that these outflows cannot be driven by current star formation alone. In the statistically reliable quiescent redshift bins at 2 ≤ z < 3 and 3 ≤ z < 4, the elevated [N II]/Hα and [O III]/Hβ ratios are consistent with a possible AGN contribution, suggesting that non-stellar feedback may play a role in sustaining quiescence in galaxies at these epochs.
ER  -

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