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Oscar Agertz. Profile photo.

Oscar Agertz

Associate Professor / Senior university lecturer / Wallenberg Academy Fellow

Oscar Agertz. Profile photo.

Cloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS-ALMA

Author

  • Adam K. Leroy
  • Jiayi Sun
  • Sharon Meidt
  • Oscar Agertz
  • I. Da Chiang
  • Jindra Gensior
  • Simon C.O. Glover
  • Oleg Y. Gnedin
  • Annie Hughes
  • Eva Schinnerer
  • Ashley T. Barnes
  • Frank Bigiel
  • Alberto D. Bolatto
  • Dario Colombo
  • Jakob den Brok
  • Mélanie Chevance
  • Ryan Chown
  • Cosima Eibensteiner
  • Damian R. Gleis
  • Kathryn Grasha
  • Jonathan D. Henshaw
  • Ralf S. Klessen
  • Eric W. Koch
  • Elias K. Oakes
  • Hsi An Pan
  • Miguel Querejeta
  • Erik Rosolowsky
  • Toshiki Saito
  • Karin Sandstrom
  • Sumit K. Sarbadhicary
  • Yu Hsuan Teng
  • Antonio Usero
  • Dyas Utomo
  • Thomas G. Williams
Show all

Summary, in English

We compare measurements of star formation efficiency to cloud-scale gas properties across the PHANGS- ALMA sample. Dividing 67 galaxies into 1.5 kpc scale regions, we calculate the molecular gas depletion time τ dep mol = Σ mol / Σ SFR and the star formation efficiency per freefall time ϵ ff mol = τ ff / τ dep mol for each region. Then we test how τ dep mol and ϵ ff mol vary as functions of the regional mass-weighted mean molecular gas properties on cloud scales (60-150 pc): gas surface density, 〈 Σ mol cloud 〉 , velocity dispersion, 〈 σ mol cloud 〉 , virial parameter, 〈 α vir cloud 〉 , and gravitational freefall time, 〈 τ ff cloud 〉 . 〈 τ ff cloud 〉 and τ dep mol correlate positively, consistent with the expectation that gas density plays a key role in setting the rate of star formation. Our fiducial measurements suggest τ dep mol ∝ 〈 τ ff cloud 〉 0.5 and ϵ ff mol ≈ 0.34 % , though the exact numbers depend on the adopted fitting methods. We also observe anticorrelations between τ dep mol and 〈 Σ mol cloud 〉 and between τ dep mol and 〈 σ mol cloud 〉 . All three correlations may reflect the same underlying link between density and star formation efficiency combined with systematic variations in the degree to which self-gravity binds molecular gas in galaxies. We highlight the τ dep mol - 〈 σ mol cloud 〉 relation because of the lower degree of correlation between the axes. Contrary to theoretical expectations, we observe an anticorrelation between τ dep mol and 〈 α vir cloud 〉 and no significant correlation between ϵ ff mol and 〈 α vir cloud 〉 . Our results depend sensitively on the adopted CO-to-H2 conversion factor, with corrections for excitation and emissivity effects in inner galaxies playing an important role. We emphasize that our simple methodology and clean selection allow for easy comparison to numerical simulations and highlight this as a logical next direction.

Department/s

  • Astrophysics

Publishing year

2025-05-20

Language

English

Publication/Series

Astrophysical Journal

Volume

985

Issue

1

Document type

Journal article

Publisher

American Astronomical Society

Topic

  • Astronomy, Astrophysics and Cosmology
  • Meteorology and Atmospheric Sciences

Status

Published

ISBN/ISSN/Other

  • ISSN: 0004-637X