ALMA-IMF: XXII. Role of core subfragmentation in the IMF origin: Hierarchical mass cascade in W43-MM1
Abstract
Aims. The gravoturbulent fragmentation of the interstellar medium is expected to create a hierarchical cascade of cloud structures, crossing the scales from core to disk. We aim to predict how the currently observed top-heavy core mass function (CMF) in the massive protocluster W43-MM1 evolves due to core subfragmentation. Methods. We used the getsf algorithm to extract sources in five ALMA images of W43-MM1 at 3 mm, with a spatial resolution ranging from 14 kau to 270 au. Then, we applied FAMILY, a graph-theory-based analysis tool, to create and characterize networks of nested sources in W43-MM1. We compared the hierarchical fragmentation cascade of W43-MM1 to those measured in the NGC 2264 protocluster and in synthetic images of an Orion-like protocluster simulated by magneto-hydrodynamical calculations. Results. Assuming self-similarity, we measured a small fractality index of F3D = 1.19 ± 0.10 in W43-MM1, which means that, on average, a cloud structure fragments into only 1.19 fragments each time the physical scale decreases by a factor of two. In line with values measured above the core scale in the NGC 2264 and synthetic protoclusters, the W43-MM1 fractality index increases by about 30% at larger scales. We also estimate an imbalanced mass partition between siblings, with two-thirds of the mass of siblings at a given scale belonging to the dominant sibling. The mass transfer efficiency, computed from one physical scale to another, is high and corresponds to a core formation efficiency (CFE) from 2400 au cores to 200 au seeds of ~16%. Conclusions. Based on the fractality and efficiency values measured in W43-MM1, the gravoturbulent model by Thomasson predicts that its fragmentation below ~14 kau is not driven by turbulence but by gravity. Using these parameters and the measured mass partition, we demonstrate that the seed mass function, from which the initial mass function (IMF) emerges, has a high-mass end that remains top-heavy. Therefore, based on our current assumptions, core subfragmentation in W43-MM1, and perhaps more broadly in massive Galactic protoclusters, plays a minimal role in shaping the high-mass slope of the IMF.
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BibTeX
@article{motte2026almaimf,
title = {{ALMA-IMF: XXII. Role of core subfragmentation in the IMF origin: Hierarchical mass cascade in W43-MM1}},
author = {F. Motte and N. Le Nestour and R. Veyry and N. Brouillet and T. Nony and B. Thomasson and F. Louvet and I. Joncour and E. Moraux and A. Men'Shchikov and T. Yoo and A. Ginsburg and A. Gusdorf and A. M. Stutz and R. Galván-Madrid and T. Csengeri and R. H. Álvarez-Gutiérrez and M. Armante and Y. Bernard and M. Bonfand and S. Chevalier and N. Cunningham and P. Dell'Ova and M. González and A. Koley and F. A. Olguin and D. Panda and Y. Pouteau and J. Salinas and P. Sanhueza and N. A. Sandoval-Garrido and M. Valeille-Manet},
journal = {Astronomy \& Astrophysics - A\&A},
year = {2026},
month = sep,
doi = {10.1051/0004-6361/202660192},
url = {https://insu.hal.science/insu-05761208v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - ALMA-IMF: XXII. Role of core subfragmentation in the IMF origin: Hierarchical mass cascade in W43-MM1
AU - F. Motte
AU - N. Le Nestour
AU - R. Veyry
AU - N. Brouillet
AU - T. Nony
AU - B. Thomasson
AU - F. Louvet
AU - I. Joncour
AU - E. Moraux
AU - A. Men'Shchikov
AU - T. Yoo
AU - A. Ginsburg
AU - A. Gusdorf
AU - A. M. Stutz
AU - R. Galván-Madrid
AU - T. Csengeri
AU - R. H. Álvarez-Gutiérrez
AU - M. Armante
AU - Y. Bernard
AU - M. Bonfand
AU - S. Chevalier
AU - N. Cunningham
AU - P. Dell'Ova
AU - M. González
AU - A. Koley
AU - F. A. Olguin
AU - D. Panda
AU - Y. Pouteau
AU - J. Salinas
AU - P. Sanhueza
AU - N. A. Sandoval-Garrido
AU - M. Valeille-Manet
PY - 2026
DA - 2026/09/23
JO - Astronomy & Astrophysics - A&A
DO - 10.1051/0004-6361/202660192
UR - https://insu.hal.science/insu-05761208v1
AB - Aims. The gravoturbulent fragmentation of the interstellar medium is expected to create a hierarchical cascade of cloud structures, crossing the scales from core to disk. We aim to predict how the currently observed top-heavy core mass function (CMF) in the massive protocluster W43-MM1 evolves due to core subfragmentation. Methods. We used the getsf algorithm to extract sources in five ALMA images of W43-MM1 at 3 mm, with a spatial resolution ranging from 14 kau to 270 au. Then, we applied FAMILY, a graph-theory-based analysis tool, to create and characterize networks of nested sources in W43-MM1. We compared the hierarchical fragmentation cascade of W43-MM1 to those measured in the NGC 2264 protocluster and in synthetic images of an Orion-like protocluster simulated by magneto-hydrodynamical calculations. Results. Assuming self-similarity, we measured a small fractality index of F3D = 1.19 ± 0.10 in W43-MM1, which means that, on average, a cloud structure fragments into only 1.19 fragments each time the physical scale decreases by a factor of two. In line with values measured above the core scale in the NGC 2264 and synthetic protoclusters, the W43-MM1 fractality index increases by about 30% at larger scales. We also estimate an imbalanced mass partition between siblings, with two-thirds of the mass of siblings at a given scale belonging to the dominant sibling. The mass transfer efficiency, computed from one physical scale to another, is high and corresponds to a core formation efficiency (CFE) from 2400 au cores to 200 au seeds of ~16%. Conclusions. Based on the fractality and efficiency values measured in W43-MM1, the gravoturbulent model by Thomasson predicts that its fragmentation below ~14 kau is not driven by turbulence but by gravity. Using these parameters and the measured mass partition, we demonstrate that the seed mass function, from which the initial mass function (IMF) emerges, has a high-mass end that remains top-heavy. Therefore, based on our current assumptions, core subfragmentation in W43-MM1, and perhaps more broadly in massive Galactic protoclusters, plays a minimal role in shaping the high-mass slope of the IMF.
SN - 0004-6361
SN - 1432-0746
ER -