Before fragmentation: from uniform clouds to stellar clusters
Abstract
Our study of the early stages of fragmentation in massive clumps has revealed a striking anomaly: ∼15% of the CoCoA sample exhibit no fragmentation at all. These sources could represent the initial conditions before core formation. We investigate whether these sources are indeed at the onset of core formation, and whether gravity or turbulence dominates their early fragmentation. We study the transition from uniform gas to active cluster formation, and compare contrasting predictions of turbulence- and gravity-dominated models of clump fragmentation through ALMA observations of three massive clumps spanning this phase. The fragmented source exhibits higher average n(H2) and a core-to-envelope density contrast 5-6 times larger than the minimally fragmented sources. All sources display pc-scale velocity differences comparable to their linewidths and gravitational velocities. This suggests that the linewidth is dominated by the large-scale motions, and that the latter are driven by gravity. The high CH3OH abundances and the mass build-up timescales align with astrochemical models where complex molecules form at intermediate densities before the appearance of cores. All independent diagnostics in our analysis are consistent with the minimally fragmented clumps being an early evolutionary phase, potentially marking the onset of core fragmentation. If turbulence were the primary driver of fragmentation, sources with comparable Mach numbers should exhibit similar structural properties. Instead, we observe significant variations in density contrast and fragmentation. These findings challenge turbulence-supported models and lend support to hierarchical, gravity-driven models of clump fragmentation, where large-scale ordered motions account for a significant fraction of the observed linewidths and drive the evolution of the clump toward increasingly dense and fragmented states.
Related
- Gas phase Elemental abundances in Molecular cloudS (GEMS). XII. First look into the para-to-ortho ratio of c-C_3D_2 towards pre-stellar cores
- A High Resolution View of Three Massive Young Stellar Objects in the Magellanic Clouds
- Cosmic Ray Diffusion and the Origin of Very High Energy Gamma-Ray Emission in Young Massive Stellar Clusters
- Dark Halos, Intermediate-Mass BH and Nuclear Stellar Clusters in Dwarf Spheroidals
- A Cosmological Framework for Stellar Collisions at High Redshift in Proto-globular Clusters, Nuclear Star Clusters, and Little Red Dots
BibTeX
@misc{giannetti2026before,
title = {{Before fragmentation: from uniform clouds to stellar clusters}},
author = {A. Giannetti and T. Pillai and J. Kauffmann and A. Palau and E. Vazquez-Semadeni and K. Morii and P. Sanhueza},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.34741},
eprint = {2609.34741},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.34741},
}
RIS
TY - UNPB
TI - Before fragmentation: from uniform clouds to stellar clusters
AU - A. Giannetti
AU - T. Pillai
AU - J. Kauffmann
AU - A. Palau
AU - E. Vazquez-Semadeni
AU - K. Morii
AU - P. Sanhueza
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.34741
UR - https://arxiv.org/abs/2609.34741
AB - Our study of the early stages of fragmentation in massive clumps has revealed a striking anomaly: ∼15% of the CoCoA sample exhibit no fragmentation at all. These sources could represent the initial conditions before core formation. We investigate whether these sources are indeed at the onset of core formation, and whether gravity or turbulence dominates their early fragmentation. We study the transition from uniform gas to active cluster formation, and compare contrasting predictions of turbulence- and gravity-dominated models of clump fragmentation through ALMA observations of three massive clumps spanning this phase. The fragmented source exhibits higher average n(H_2) and a core-to-envelope density contrast 5-6 times larger than the minimally fragmented sources. All sources display pc-scale velocity differences comparable to their linewidths and gravitational velocities. This suggests that the linewidth is dominated by the large-scale motions, and that the latter are driven by gravity. The high CH_3OH abundances and the mass build-up timescales align with astrochemical models where complex molecules form at intermediate densities before the appearance of cores. All independent diagnostics in our analysis are consistent with the minimally fragmented clumps being an early evolutionary phase, potentially marking the onset of core fragmentation. If turbulence were the primary driver of fragmentation, sources with comparable Mach numbers should exhibit similar structural properties. Instead, we observe significant variations in density contrast and fragmentation. These findings challenge turbulence-supported models and lend support to hierarchical, gravity-driven models of clump fragmentation, where large-scale ordered motions account for a significant fraction of the observed linewidths and drive the evolution of the clump toward increasingly dense and fragmented states.
ER -