ALMAGAL

Astronomy and Astrophysics, vol. 707, pp. A221

Abstract

Context . High-mass stars and star clusters form from the fragmentation of massive dense clumps driven by gravity, turbulence, and magnetic fields. The extent to which each of these agents impacts the fragmentation depending on the clump mass, density, and evolutionary stage is still largely unknown. Aims . The ALMA evolutionary study of high-mass protocluster formation in the GALaxy (ALMAGAL) project, with ∼1000 clumps observed at ∼1000 au resolution, allows a statistically significant characterization of the fragmentation process over a large range of clump physical parameters and evolutionary stages. Our goal is to characterize where and how the dense cores revealed by ALMA are distributed in massive potentially cluster-forming clumps to trace how fragmentation is initially set and how it proceeds before gas dispersal due to stellar feedback. Methods . We characterized the spatial distribution of dense cores in the 514 ALMAGAL clumps that host at least four cores, using a set of quantitative descriptors that we evaluated against the clump bolometric luminosity-to-mass ratio, which we adopted as an indicator of the evolution of the system. We measured the separations between cores with the minimum spanning tree (MST) method, which we compared with the predictions of gravitational fragmentation from Jeans theory. We investigated whether cores have specific arrangements using the Q parameter or variations due to their masses with the mass segregation ratio, Λ MSR . Results . ALMAGAL cores are distributed throughout the entire area of the clump, usually arranged in elliptical groups with an axis ratio e ∼2.2, although high values with e ≥ 5 are also observed. We found a single characteristic core separation per clump in ∼76% of cases, suggesting that multiple fragmentation lengths may be frequently present. Typical core separations are compatible with the clump-averaged thermal Jeans length, λ J th . However, we found an additional population of cores, typical of low-fragmented and young clumps, which are on average more widely separated with l ≈ 3 × λ J th . By stacking the distributions of the core separations in clumps of similar evolutionary stage, we also found that the separation decreases on average from l ∼22 000 au in younger systems to l ∼7000 au in more evolved ones. The ALMAGAL cores are typically distributed in fractal-type subclusters, while centrally concentrated patterns appear only at later stages, but we do not observe a progressive transition between these configurations with evolution. Finally, we also found 110 ALMAGAL systems with a signature of mass segregation, with an occurrence that increases with evolution.

Authors 45

1. E. Schisano

   Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

   Affiliation as printed

   INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

2. S. Molinari

   Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

   Affiliation as printed

   INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

3. Antonella Coletta

   Institute for Space Astrophysics and Planetology · Sapienza University of Rome · National Institute for Astrophysics

   Affiliation as printed

   Dipartimento di Fisica, Sapienza Università di Roma

   INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

4. Davide Elia

   Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

   Affiliation as printed

   INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

5. P. Schilke

   University of Cologne

   Affiliation as printed

   Physikalisches Institut der Universität zu Köln

6. A. Traficante

   Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

   Affiliation as printed

   INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

7. Á. Sánchez-Monge

   Institute of Space Sciences · Consejo Superior de Investigaciones Científicas · Institut d'Estudis Espacials de Catalunya

   Affiliation as printed

   Institut de Ciències de l’Espai (ICE, CSIC)

   Institut d’Estudis Espacials de Catalunya (IEEC)

8. Henrik Beuther

   Max Planck Institute for Astronomy

   Affiliation as printed

   Max Planck Institute for Astronomy

9. M. Benedettini

   Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

   Affiliation as printed

   INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

10. C. Mininni

    Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

    Affiliation as printed

    INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

11. Ralf Stephan Klessen

    Harvard University · Heidelberg University · Center for Astrophysics Harvard & Smithsonian

    Affiliation as printed

    Center for Astrophysics, Harvard & Smithsonian

    Radcliffe Institute for Advanced Studies at Harvard University

    Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen

    Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik

12. Juan Diego Soler

    Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

    Affiliation as printed

    INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

13. S. Pezzuto

    Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

    Affiliation as printed

    INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

14. Floris F. S. van der Tak Aachen SRON Netherlands Institute for Space Research

    University of Groningen · Space Research Organisation Netherlands

    Affiliation as printed

    Kapteyn Astronomical Institute, University of Groningen

    SRON Netherlands Institute for Space Research

15. P. Hennebelle

    Centre National de la Recherche Scientifique · Université Paris Cité · Commissariat à l'Énergie Atomique et aux Énergies Alternatives · Université Paris-Saclay · CEA Paris-Saclay

    Affiliation as printed

    Université Paris-Saclay, Université Paris-Cité, CEA, CNRS

16. M. T. Beltrán

    National Institute for Astrophysics

    Affiliation as printed

    Istituto Nazionale di Astrofisica (INAF)

17. L. Moscadelli

    National Institute for Astrophysics

    Affiliation as printed

    Istituto Nazionale di Astrofisica (INAF)

18. Kazi L. J. Rygl

    National Institute for Astrophysics

    Affiliation as printed

    INAF-Istituto di Radioastronomia & Italian ALMA Regional center

19. Patricio Sanhueza

    The University of Tokyo

    Affiliation as printed

    Department of Astronomy, School of Science, The University of Tokyo

20. D. C. Lis

    Jet Propulsion Laboratory

    Affiliation as printed

    Jet Propulsion Laboratory, California Institute of Technology

21. Rolf Kuiper

    University of Duisburg-Essen

    Affiliation as printed

    Faculty of Physics, University of Duisburg-Essen

22. G. A. Fuller

    University of Cologne · University of Manchester

    Affiliation as printed

    Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester

    Physikalisches Institut der Universität zu Köln

23. A. Avison

    SKA Observatory

    Affiliation as printed

    SKA Observatory

24. L. Bronfman

    University of Chile

    Affiliation as printed

    Departamento de Astronomía, Universidad de Chile

25. U. Lebreuilly

    Centre National de la Recherche Scientifique · Université Paris Cité · Commissariat à l'Énergie Atomique et aux Énergies Alternatives · Université Paris-Saclay · CEA Paris-Saclay

    Affiliation as printed

    Université Paris-Saclay, Université Paris-Cité, CEA, CNRS

26. T. Möller

    University of Cologne

    Affiliation as printed

    Physikalisches Institut der Universität zu Köln

27. V.-M. Pelkonen

    Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

    Affiliation as printed

    INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

28. L. Testi

    University of Bologna

    Affiliation as printed

    Dipartimento di Fisica e Astronomia, Alma Mater Studiorium Università di Bologna Dipartimento di Fisica e Astronomia “Augusto Righi”

29. Tianwei Zhang

    University of Cologne · Zhejiang Lab

    Affiliation as printed

    Physikalisches Institut der Universität zu Köln

    Research Center for Astronomical computing, Zhejiang Laboratory

30. Aida Ahmadi Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University

31. J. Allande

    University of Florence · National Institute for Astrophysics

    Affiliation as printed

    Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze

    Istituto Nazionale di Astrofisica (INAF)

32. C. Battersby

    University of Connecticut

    Affiliation as printed

    University of Connecticut, Department of Physics

33. J. Wallace

    University of Connecticut

    Affiliation as printed

    University of Connecticut, Department of Physics

34. C. L. Brogan

    National Radio Astronomy Observatory

    Affiliation as printed

    National Radio Astronomy Observatory

35. F. De Angelis

    Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

    Affiliation as printed

    INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

36. F. Fontani

    Max Planck Society · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Université · Max Planck Institute for Extraterrestrial Physics · National Institute for Astrophysics

    Affiliation as printed

    Istituto Nazionale di Astrofisica (INAF)

    LUX, Observatoire de Paris, Université PSL, Sorbonne Université

    Max-Planck-Institute for Extraterrestrial Physics (MPE)

37. Paul T. P. Ho

    Institute of Astronomy and Astrophysics, Academia Sinica · East Asian Observatory

    Affiliation as printed

    East Asian Observatory

    Institute of Astronomy and Astrophysics

38. T. R. Hunter

    National Radio Astronomy Observatory

    Affiliation as printed

    National Radio Astronomy Observatory

39. K. Johnston

    University of Lincoln

    Affiliation as printed

    School of Engineering and Physical Sciences, The University of Lincoln

40. P. D. Klaassen

    Royal Observatory · UK Astronomy Technology Centre

    Affiliation as printed

    UK Astronomy Technology center, Royal Observatory Edinburgh

41. S. -Y. Liu

    Institute of Astronomy and Astrophysics, Academia Sinica · Institute for Space Astrophysics and Planetology · National Institute for Astrophysics

    Affiliation as printed

    INAF – IAPS, via Fosso del Cavaliere, 100, 00133 Roma, Italy; Istituto Nazionale di Astrofisica (INAF)-Istituto di Astrofisica e Planetologia Spaziali

    Institute of Astronomy and Astrophysics

42. Y. Maruccia

    Astronomical Observatory of Capodimonte · National Institute for Astrophysics

    Affiliation as printed

    INAF – Astronomical Observatory of Capodimonte

43. A. J. Rigby

    University of Leeds

    Affiliation as printed

    School of Physics and Astronomy, University of Leeds

44. Yu‐Nung Su

    Institute of Astronomy and Astrophysics, Academia Sinica

    Affiliation as printed

    Institute of Astronomy and Astrophysics

45. H. Zinnecker

    Universidad Autónoma de Chile

    Affiliation as printed

    Universidad Autónoma de Chile