Unveiling the Origins of the Molecular Gas Reservoirs in Recently Quenched Massive Galaxies

Abstract

Observations of quenched galaxies across cosmic time have revealed systems containing substantial molecular gas reservoirs, challenging the traditional picture of gas-poor, red and dead galaxies. Using the Simba cosmological simulation, we investigate three possible hypotheses for the origin of molecular gas-rich quenched systems: (i) quiescence is temporary and the galaxy will rejuvenate, (ii) molecular gas masses are overestimated due to an underestimated CO-to-H₂ conversion factor, or (iii) star formation is ongoing but heavily obscured by dust. Across M_*>3×10⁹M_⊙ galaxies from z=0−2, we find that all three mechanisms are plausible. Many seemingly quiescent, molecular gas-rich galaxies host dust-obscured star formation, with visual optical depths increasing on average from τ_V∼0.5−2.3 from z=0−2. Assuming a Milky Way-like CO-to-H₂ conversion factor can overestimate molecular gas masses by a factor of ∼ 5 in non-star-forming galaxies, compared to ∼ 1.45 in star-forming galaxies. Temporary quiescence can also occur in gas-rich transitioning galaxies on timescales ranging from 100 Myr−2 Gyr, although this is most prominent at high redshift and is relatively rare overall. Further work is needed to disentangle the relative contributions of these mechanisms across cosmic time.

Extreme MgII Emission in Recently-Quenched Galaxies: A New Sample of Intermediate-Redshift Post-Starburst Quasars from the DESI Early Data Release
Margaret E. Verrico, Aayan Verma, K. Decker French +8
arXiv28 Sep 2026PreprintCC BY 4.0Full textGalaxiesarXiv
Euclid Quick Data Release (Q1). Exploring the complexity of quenching processes across time, environment, and mass through recently quenched galaxies
Euclid Collaboration, Z. Mao, L. Pozzetti +308
arXiv6 Oct 2026PreprintCC BY 4.0Full textGalaxiesarXiv
Unveiling the population of massive quenched galaxies at z≥2 in the COLIBRE simulations - II. The role of AGN feedback and environment on their emergence
Ángel Chandro-Gómez, Claudia del P. Lagos, Chris Power +16
arXiv10 Sep 2026PreprintCC BY 4.0Full textGalaxiesarXiv
Discovery of Isolated, Quenched Candidate Backsplash Dwarf Galaxies near M101
Julian Shapiro
The Astrophysical Journal6 Oct 2026Peer-reviewedCC BY 4.0Full textGalaxiesCrossref
Unveiling the hot interstellar medium in nearby galaxies with eROSITA
Roman Laktionov, Manami Sasaki, Elias Kyritsis +9
Astronomy & Astrophysics22 Oct 2026Peer-reviewedPublisher termsGalaxiesCrossref

Cite

BibTeX RIS

BibTeX

@misc{savitch2026unveiling,
  title = {{Unveiling the Origins of the Molecular Gas Reservoirs in Recently Quenched Massive Galaxies}},
  author = {E. Savitch and D. Narayanan and D. J. Setton and K. E. Whitaker and R. Bezanson and E. Cenci and R. Davé and V. R. D'Onofrio and R. Feldmann and J. E. Greene and M. Kriek and M. Parente and J. S. Spilker and K. A. Suess and D. Valentín-Martínez and D. Zimmerman},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.06680},
  eprint = {2610.06680},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.06680},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Unveiling the Origins of the Molecular Gas Reservoirs in Recently Quenched Massive Galaxies
AU  - E. Savitch
AU  - D. Narayanan
AU  - D. J. Setton
AU  - K. E. Whitaker
AU  - R. Bezanson
AU  - E. Cenci
AU  - R. Davé
AU  - V. R. D'Onofrio
AU  - R. Feldmann
AU  - J. E. Greene
AU  - M. Kriek
AU  - M. Parente
AU  - J. S. Spilker
AU  - K. A. Suess
AU  - D. Valentín-Martínez
AU  - D. Zimmerman
PY  - 2026
DA  - 2026/10/05
PB  - arXiv
DO  - 10.48550/arxiv.2610.06680
UR  - https://arxiv.org/abs/2610.06680
AB  - Observations of quenched galaxies across cosmic time have revealed systems containing substantial molecular gas reservoirs, challenging the traditional picture of gas-poor, red and dead galaxies. Using the Simba cosmological simulation, we investigate three possible hypotheses for the origin of molecular gas-rich quenched systems: (i) quiescence is temporary and the galaxy will rejuvenate, (ii) molecular gas masses are overestimated due to an underestimated CO-to-H_2 conversion factor, or (iii) star formation is ongoing but heavily obscured by dust. Across M_*>3×10^9M_⊙ galaxies from z=0−2, we find that all three mechanisms are plausible. Many seemingly quiescent, molecular gas-rich galaxies host dust-obscured star formation, with visual optical depths increasing on average from τ_V∼0.5−2.3 from z=0−2. Assuming a Milky Way-like CO-to-H_2 conversion factor can overestimate molecular gas masses by a factor of ∼ 5 in non-star-forming galaxies, compared to ∼ 1.45 in star-forming galaxies. Temporary quiescence can also occur in gas-rich transitioning galaxies on timescales ranging from 100 Myr−2 Gyr, although this is most prominent at high redshift and is relatively rare overall. Further work is needed to disentangle the relative contributions of these mechanisms across cosmic time.
ER  -

Abstract

Related

Cite