Cloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS–ALMA
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 ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}={{\rm{\Sigma }}}_{{\rm{mol}}}/{{\rm{\Sigma }}}_{{\rm{SF...
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| 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 |
| author_facet | 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 |
| author_sort | Adam K. Leroy |
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| description | 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 ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}={{\rm{\Sigma }}}_{{\rm{mol}}}/{{\rm{\Sigma }}}_{{\rm{SFR}}}$ and the star formation efficiency per freefall time ${\epsilon }_{{\rm{ff}}}^{{\rm{mol}}}={\tau }_{{\rm{ff}}}/{\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ for each region. Then we test how ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ and ${\epsilon }_{{\rm{ff}}}^{{\rm{mol}}}$ vary as functions of the regional mass-weighted mean molecular gas properties on cloud scales (60–150 pc): gas surface density, $\langle {{\rm{\Sigma }}}_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ , velocity dispersion, $\langle {\sigma }_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ , virial parameter, $\langle {\alpha }_{{\rm{vir}}}^{{\rm{cloud}}}\rangle $ , and gravitational freefall time, $\langle {\tau }_{{\rm{ff}}}^{{\rm{cloud}}}\rangle $ . $\langle {\tau }_{{\rm{ff}}}^{{\rm{cloud}}}\rangle $ and ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ correlate positively, consistent with the expectation that gas density plays a key role in setting the rate of star formation. Our fiducial measurements suggest ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}\propto {\langle {\tau }_{{\rm{ff}}}^{{\rm{cloud}}}\rangle }^{0.5}$ and ${\epsilon }_{{\rm{ff}}}^{{\rm{mol}}}\approx 0.34 \% $ , though the exact numbers depend on the adopted fitting methods. We also observe anticorrelations between ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ and $\langle {{\rm{\Sigma }}}_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ and between ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ and $\langle {\sigma }_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ . 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 ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ – $\langle {\sigma }_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ relation because of the lower degree of correlation between the axes. Contrary to theoretical expectations, we observe an anticorrelation between ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ and $\langle {\alpha }_{{\rm{vir}}}^{{\rm{cloud}}}\rangle $ and no significant correlation between ${\epsilon }_{{\rm{ff}}}^{{\rm{mol}}}$ and $\langle {\alpha }_{{\rm{vir}}}^{{\rm{cloud}}}\rangle $ . Our results depend sensitively on the adopted CO-to-H _2 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. |
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| spelling | doaj-art-ccc7de768dc849daa40b47ae6e813e3f2025-08-20T01:50:26ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198511410.3847/1538-4357/adbcabCloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS–ALMAAdam K. Leroy0https://orcid.org/0000-0002-2545-1700Jiayi Sun1https://orcid.org/0000-0003-0378-4667Sharon Meidt2https://orcid.org/0000-0002-6118-4048Oscar Agertz3https://orcid.org/0000-0002-4287-1088I-Da Chiang4https://orcid.org/0000-0003-2551-7148Jindra Gensior5https://orcid.org/0000-0001-6119-9883Simon C. O. Glover6https://orcid.org/0000-0001-6708-1317Oleg Y. Gnedin7https://orcid.org/0000-0001-9852-9954Annie Hughes8https://orcid.org/0000-0002-9181-1161Eva Schinnerer9https://orcid.org/0000-0002-3933-7677Ashley T. Barnes10https://orcid.org/0000-0003-0410-4504Frank Bigiel11https://orcid.org/0000-0003-0166-9745Alberto D. Bolatto12https://orcid.org/0000-0002-5480-5686Dario Colombo13https://orcid.org/0000-0001-6498-2945Jakob den Brok14https://orcid.org/0000-0002-8760-6157Mélanie Chevance15https://orcid.org/0000-0002-5635-5180Ryan Chown16https://orcid.org/0000-0001-8241-7704Cosima Eibensteiner17https://orcid.org/0000-0002-1185-2810Damian R. Gleis18https://orcid.org/0009-0001-8660-9962Kathryn Grasha19https://orcid.org/0000-0002-3247-5321Jonathan D. Henshaw20https://orcid.org/0000-0001-9656-7682Ralf S. Klessen21https://orcid.org/0000-0002-0560-3172Eric W. Koch22https://orcid.org/0000-0001-9605-780XElias K. Oakes23https://orcid.org/0000-0002-0119-1115Hsi-An Pan24https://orcid.org/0000-0002-1370-6964Miguel Querejeta25https://orcid.org/0000-0002-0472-1011Erik Rosolowsky26https://orcid.org/0000-0002-5204-2259Toshiki Saito27Karin Sandstrom28https://orcid.org/0000-0002-4378-8534Sumit K. Sarbadhicary29https://orcid.org/0000-0002-4781-7291Yu-Hsuan Teng30https://orcid.org/0000-0003-4209-1599Antonio Usero31https://orcid.org/0000-0003-1242-505XDyas Utomo32Thomas G. Williams33https://orcid.org/0000-0002-0012-2142Department of Astronomy, The Ohio State University , 140 West 18th Avenue, Columbus, OH 43210, USA ; leroy.42@osu.edu; Center for Cosmology and Astroparticle Physics (CCAPP) , 191 West Woodruff Avenue, Columbus, OH 43210, USADepartment of Astrophysical Sciences, Princeton University , 4 Ivy Lane, Princeton, NJ 08544, USASterrenkundig Observatorium, Universiteit Gent , Krijgslaan 281 S9, B-9000 Gent, BelgiumLund Observatory, Division of Astrophysics, Department of Physics, Lund University , Box 43, SE-221 00 Lund, SwedenInstitute of Astronomy and Astrophysics , Academia Sinica, No. 1, Sec. 4, Roosevelt Road, Taipei 106319, TaiwanInstitute for Astronomy, University of Edinburgh , Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK; Department of Astrophysics, University of Zürich , Winterthurerstrasse 190, 8057 Zürich, SwitzerlandUniversität Heidelberg , Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str 2, D-69120 Heidelberg, GermanyDepartment of Astronomy, University of Michigan , Ann Arbor, MI 48109, USACNRS , IRAP, 9 Av. du Colonel Roche, BP 44346, F-31028 Toulouse cedex 4, FranceMax-Planck-Institut für Astronomie , Königstuhl 17, D-69117, Heidelberg, GermanyEuropean Southern Observatory , Karl-Schwarzschild Straße 2, D-85748 Garching bei München, GermanyArgelander-Institut für Astronomie, Universität Bonn , Auf dem Hügel 71, 53121 Bonn, GermanyDepartment of Astronomy and Joint Space-Science Institute, University of Maryland , 4296 Stadium Drive, College Park, MD 20742, USAArgelander-Institut für Astronomie, Universität Bonn , Auf dem Hügel 71, 53121 Bonn, GermanyCenter for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USAUniversität Heidelberg , Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str 2, D-69120 Heidelberg, Germany; Cosmic Origins Of Life (COOL) Research DAO , GermanyDepartment of Astronomy, The Ohio State University , 140 West 18th Avenue, Columbus, OH 43210, USA ; leroy.42@osu.eduNational Radio Astronomy Observatory , 520 Edgemont Road, Charlottesville, VA 22903, USAMax-Planck-Institut für Astronomie , Königstuhl 17, D-69117, Heidelberg, GermanyResearch School of Astronomy and Astrophysics, Australian National University , Canberra, ACT 2611, AustraliaMax-Planck-Institut für Astronomie , Königstuhl 17, D-69117, Heidelberg, Germany; Astrophysics Research Institute, Liverpool John Moores University , IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UKUniversität Heidelberg , Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str 2, D-69120 Heidelberg, Germany; Center for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USA; Universität Heidelberg , Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Im Neuenheimer Feld 205, D-69120 Heidelberg, Germany; Radcliffe Institute for Advanced Studies at Harvard University , 10 Garden Street, Cambridge, MA 02138, USACenter for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USADepartment of Physics, University of Connecticut , 196A Auditorium Road, Storrs, CT 06269, USADepartment of Physics, Tamkang University , No.151, Yingzhuan Road, Tamsui Dist., New Taipei City 251301, TaiwanObservatorio Astronómico Nacional (IGN) , C/Alfonso XII, 3, E-28014 Madrid, SpainDepartment of Physics, University of Alberta , Edmonton, AB T6G 2E1, CanadaFaculty of Global Interdisciplinary Science and Innovation, Shizuoka University , 836 Ohya, Suruga-ku, Shizuoka 422-8529, JapanCenter for Astrophysics and Space Sciences, Department of Physics, University of California , San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USADepartment of Astronomy, The Ohio State University , 140 West 18th Avenue, Columbus, OH 43210, USA ; leroy.42@osu.edu; Center for Cosmology and Astroparticle Physics (CCAPP) , 191 West Woodruff Avenue, Columbus, OH 43210, USA; Department of Physics, The Ohio State University , Columbus, Ohio 43210, USADepartment of Astronomy and Joint Space-Science Institute, University of Maryland , 4296 Stadium Drive, College Park, MD 20742, USAObservatorio Astronómico Nacional (IGN) , C/Alfonso XII, 3, E-28014 Madrid, SpainDepartment of Astronomy, The Ohio State University , 140 West 18th Avenue, Columbus, OH 43210, USA ; leroy.42@osu.edu; National Radio Astronomy Observatory , 520 Edgemont Road, Charlottesville, VA 22903, USASub-department of Astrophysics, Department of Physics, University of Oxford , Keble Road, Oxford OX1 3RH, UKWe 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 ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}={{\rm{\Sigma }}}_{{\rm{mol}}}/{{\rm{\Sigma }}}_{{\rm{SFR}}}$ and the star formation efficiency per freefall time ${\epsilon }_{{\rm{ff}}}^{{\rm{mol}}}={\tau }_{{\rm{ff}}}/{\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ for each region. Then we test how ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ and ${\epsilon }_{{\rm{ff}}}^{{\rm{mol}}}$ vary as functions of the regional mass-weighted mean molecular gas properties on cloud scales (60–150 pc): gas surface density, $\langle {{\rm{\Sigma }}}_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ , velocity dispersion, $\langle {\sigma }_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ , virial parameter, $\langle {\alpha }_{{\rm{vir}}}^{{\rm{cloud}}}\rangle $ , and gravitational freefall time, $\langle {\tau }_{{\rm{ff}}}^{{\rm{cloud}}}\rangle $ . $\langle {\tau }_{{\rm{ff}}}^{{\rm{cloud}}}\rangle $ and ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ correlate positively, consistent with the expectation that gas density plays a key role in setting the rate of star formation. Our fiducial measurements suggest ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}\propto {\langle {\tau }_{{\rm{ff}}}^{{\rm{cloud}}}\rangle }^{0.5}$ and ${\epsilon }_{{\rm{ff}}}^{{\rm{mol}}}\approx 0.34 \% $ , though the exact numbers depend on the adopted fitting methods. We also observe anticorrelations between ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ and $\langle {{\rm{\Sigma }}}_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ and between ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ and $\langle {\sigma }_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ . 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 ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ – $\langle {\sigma }_{{\rm{mol}}}^{{\rm{cloud}}}\rangle $ relation because of the lower degree of correlation between the axes. Contrary to theoretical expectations, we observe an anticorrelation between ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ and $\langle {\alpha }_{{\rm{vir}}}^{{\rm{cloud}}}\rangle $ and no significant correlation between ${\epsilon }_{{\rm{ff}}}^{{\rm{mol}}}$ and $\langle {\alpha }_{{\rm{vir}}}^{{\rm{cloud}}}\rangle $ . Our results depend sensitively on the adopted CO-to-H _2 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.https://doi.org/10.3847/1538-4357/adbcabStar formationDisk galaxiesInterstellar mediumMolecular gas |
| spellingShingle | 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 Cloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS–ALMA The Astrophysical Journal Star formation Disk galaxies Interstellar medium Molecular gas |
| title | Cloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS–ALMA |
| title_full | Cloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS–ALMA |
| title_fullStr | Cloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS–ALMA |
| title_full_unstemmed | Cloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS–ALMA |
| title_short | Cloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS–ALMA |
| title_sort | cloud scale gas properties depletion times and star formation efficiency per freefall time in phangs alma |
| topic | Star formation Disk galaxies Interstellar medium Molecular gas |
| url | https://doi.org/10.3847/1538-4357/adbcab |
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