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Journal Articles Monthly Notices of the Royal Astronomical Society Year : 2020

The lifecycle of molecular clouds in nearby star-forming disc galaxies

Mélanie Chevance
J. M. Diederik Kruijssen
  • Function : Author
Alexander P. S. Hygate
  • Function : Author
Andreas Schruba
  • Function : Author
Steven N. Longmore
  • Function : Author
Brent Groves
Jonathan D. Henshaw
  • Function : Author
Cinthya N. Herrera
  • Function : Author
Sarah M. R. Jeffreson
  • Function : Author
Philipp Lang
  • Function : Author
Adam K. Leroy
  • Function : Author
Sharon E. Meidt
  • Function : Author
Jérôme Pety
Alessandro Razza
Erik Rosolowsky
Eva Schinnerer
Frank Bigiel
Guillermo A. Blanc
  • Function : Author
Christopher M. Faesi
  • Function : Author
Simon C. O. Glover
  • Function : Author
Daniel T. Haydon
  • Function : Author
I. -Ting Ho
  • Function : Author
Kathryn Kreckel
Janice C. Lee
  • Function : Author
Daizhong Liu
Miguel Querejeta
Toshiki Saito
Jiayi Sun
Antonio Usero
Dyas Utomo


It remains a major challenge to derive a theory of cloud-scale (≲100 pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially resolved (∼100 pc) CO-to-H α flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically 10-30 Myr, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities Σ _H_2≥8 M_⊙ pc^{-2}, the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at Σ _H_2≤8 M_⊙ pc^{-2} GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by H α (75-90 per cent of the cloud lifetime), GMCs disperse within just 1-5 Myr once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4-10 per cent. These results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. GMCs and H II regions are the fundamental units undergoing these lifecycles, with mean separations of 100-300 pc in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles.
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insu-03673154 , version 1 (20-05-2022)



Mélanie Chevance, J. M. Diederik Kruijssen, Alexander P. S. Hygate, Andreas Schruba, Steven N. Longmore, et al.. The lifecycle of molecular clouds in nearby star-forming disc galaxies. Monthly Notices of the Royal Astronomical Society, 2020, 493, pp.2872-2909. ⟨10.1093/mnras/stz3525⟩. ⟨insu-03673154⟩
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