Massive star cluster formation

Astronomy and Astrophysics, vol. 690, pp. A94

Abstract

The mode of star formation that results in the formation of globular clusters and young massive clusters is difficult to constrain through observations. We present models of massive star cluster formation using the TORCH framework, which uses the Astrophysical MUltipurpose Software Environment (AMUSE) to couple distinct multi-physics codes that handle star formation, stellar evolution and dynamics, radiative transfer, and magnetohydrodynamics. We upgraded TORCH by implementing the N-body code PETAR, thereby enabling TORCH to handle massive clusters forming from 106 M⊙ clouds with ≥105 individual stars. We present results from TORCH simulations of star clusters forming from 104, 105, and 106 M⊙ turbulent spherical gas clouds (named M4, M5, M6) of radius R = 11.7 pc. We find that star formation is highly efficient and becomes more so at a higher cloud mass and surface density. For M4, M5, and M6 with initial surface densities 2.325 × 101,2,3 M⊙ pc−2, after a free-fall time of tff = 6.7,2.1,0.67 Myr, we find that ∼30%, 40%, and 60% of the cloud mass has formed into stars, respectively. The end of simulation-integrated star formation efficiencies for M4, M5, and M6 are ϵ⋆ = M⋆/Mcloud = 36%, 65%, and 85%. Observations of nearby clusters similar in mass and size to M4 have instantaneous star formation efficiencies of ϵinst ≤ 30%, which is slightly lower than the integrated star formation efficiency of M4. The M5 and M6 models represent a different regime of cluster formation that is more appropriate for the conditions in starburst galaxies and gas-rich galaxies at high redshift, and that leads to a significantly higher efficiency of star formation. We argue that young massive clusters build up through short efficient bursts of star formation in regions that are sufficiently dense (Σ ≥ 102 M⊙ pc−2) and massive (Mcloud ≥ 105 M⊙). In such environments, stellar feedback from winds and radiation is not strong enough to counteract the gravity from gas and stars until a majority of the gas has formed into stars.

Authors 15

1. Brooke Polak

   American Museum of Natural History · Heidelberg University

   Affiliation as printed

   Department of Astrophysics, American Museum of Natural History, New York, NY, USA

   Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Heidelberg, Germany

2. Mordecai‐Mark Mac Low

   American Museum of Natural History · Drexel University

   Affiliation as printed

   Department of Astrophysics, American Museum of Natural History, New York, NY, USA

   Department of Physics, Drexel University, Philadelphia, PA, USA

3. Ralf Stephan Klessen

   Heidelberg University

   Affiliation as printed

   Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Heidelberg, Germany

   Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Heidelberg, Germany

4. Jia Wei Teh

   Heidelberg University

   Affiliation as printed

   Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Heidelberg, Germany

5. Claude Cournoyer-Cloutier

   McMaster University

   Affiliation as printed

   Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada

6. Eric P. Andersson

   American Museum of Natural History

   Affiliation as printed

   Department of Astrophysics, American Museum of Natural History, New York, NY, USA

7. Sabrina M. Appel

   Rutgers, The State University of New Jersey

   Affiliation as printed

   Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, USA

8. Aaron Tran

   University of Wisconsin–Madison

   Affiliation as printed

   Department of Physics, University of Wisconsin–Madison, Madison, WI, USA

9. Sean C. Lewis

   Drexel University

   Affiliation as printed

   Department of Physics, Drexel University, Philadelphia, PA, USA

10. Maite J. C. Wilhelm Aachen Sterrewacht Leiden

    Leiden University · Leiden Observatory

    Affiliation as printed

    Sterrewacht Leiden, Leiden University, Leiden, The Netherlands

11. Simon Portegies Zwart Aachen Sterrewacht Leiden

    Leiden University · Leiden Observatory

    Affiliation as printed

    Sterrewacht Leiden, Leiden University, Leiden, The Netherlands

12. Simon C. O. Glover

    Heidelberg University

    Affiliation as printed

    Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Heidelberg, Germany

13. Steven Rieder

    KU Leuven

    Affiliation as printed

    Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium

14. Long Wang

    Sun Yat-sen University

    Affiliation as printed

    School of Physics and Astronomy, Sun Yat-sen University, Daxue Road, Zhuhai 519082, China

15. Stephen L. W. McMillan

    Drexel University

    Affiliation as printed

    Department of Physics, Drexel University, Philadelphia, PA, USA