ALMAGAL

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.

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Journal
Astronomy and Astrophysics
Published
2026-01-30
DOI
https://doi.org/10.1051/0004-6361/202555619
Primary Topic
Astrophysics and Star Formation Studies
Type
article
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article

ALMAGAL

P. Schilke, A. Avison, A. Coletta, V.-M. Pelkonen et al.
Astronomy and Astrophysics
Astrophysics and Star Formation Studies
article

ALMAGAL

P. Schilke, A. Avison, A. Coletta, V.-M. Pelkonen, T. Möller, Stephen P. Walch, A. Nucara, G. A. Fuller, Paul T. P. Ho, C. Battersby, J. Wallace, K. L. J. Rygl, A. J. Rigby, Yuan Tang, Y. Maruccia, P. Sanhueza, M. T. Beltrán, F. Fontani, C. Mininni, D. C. Lis, Á. Sánchez-Monge, S. Pezzuto, H. Zinnecker, C. L. Brogan, A. Traficante, K. Johnston, L. Testi, Stéphanie Clarke, H. Beuther, Ralf S. Klessen, T. R. Hunter, M. Benedettini, L. Bronfman, U. Lebreuilly, S. -Y. Liu, D. Elia, L. Moscadelli, S. Molinari, A. Ahmadi, F. van der Tak, T. Zhang, R. Kuiper, Peter Koch, Ting Liu, Qin Zhang, F. De Angelis, Yu‐Nung Su, P. D. Klaassen, J. D. Soler, P. Hennebelle, B. F. Jones, Siqing Liu, E. Schisano, J. Allande
article en

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.

Astronomy and AstrophysicsVol. 707
University of Rome Tor Vergata (IT), Leiden University (NL), Centre National de la Recherche Scientifique (FR), University of Leeds (GB), Institute of Astronomy and Astrophysics, Academia Sinica (TW), Institute of Space Sciences (ES), Jet Propulsion Laboratory (US), University of Connecticut (US), University of Groningen (NL), University of Cologne (DE), Université Paris Cité (FR), Heidelberg University (DE), National Radio Astronomy Observatory (US), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris Sciences et Lettres (FR), Université Paris-Saclay (FR), Shanghai Astronomical Observatory (CN), Astronomical Observatory of Capodimonte (IT), John Radcliffe Hospital (GB), University of Manchester (GB), Universidad Autónoma de Chile (CL), Sorbonne Université (FR), Max Planck Institute for Extraterrestrial Physics (DE), Institut d'Estudis Espacials de Catalunya (ES), Institute for Space Astrophysics and Planetology (IT), SKA Observatory (GB), Max Planck Institute for Astronomy (DE), Istituto di Radioastronomia di Bologna (IT), East Asian Observatory (US), Zhejiang Lab (CN), Forschungsstätte der Evangelischen Studiengemeinschaft (DE), Center for Astrophysics Harvard & Smithsonian (US), CEA Paris-Saclay (FR), Astronomical Institute of the Slovak Academy of Sciences (SK), Istituto Nazionale per la Fisica della Materia (IT), University of Florence (IT), Space Research Organisation Netherlands (NL), UK Astronomy Technology Centre (GB), University of Lincoln (GB), University of Duisburg-Essen (DE), University of Chile (CL), The University of Tokyo (JP), Sapienza University of Rome (IT), National Institute for Astrophysics (IT), University of Bologna (IT)
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Astrophysics and Star Formation Studies
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