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1. ALMAGAL: V. Relations between the core populations and the parent clump physical properties

   https://doi.org/10.1051/0004-6361/202554764  

   Elia, D; Coletta, A; Molinari, S; Schisano, E; Benedettini, M; Sánchez-Monge, Á; Traficante, A; Mininni, C; Nucara, A; Pezzuto, S; et al (January 2026, Astronomy & Astrophysics)

   Context. The fragmentation of massive molecular clumps into smaller, potentially star-forming cores plays a key role in the processes of high-mass star formation. The ALMAGAL project, using the Atacama Large Millimeter/submillimeter Array (ALMA), offers highr-esolution data to investigate these processes across various evolutionary stages in the Galactic plane. Aims. This study aims at correlating the fragmentation properties of massive clumps, obtained from ALMA observations, with their global physical parameters (e.g., mass, surface density, and temperature) and evolutionary indicators (e.g., luminosity-to-mass ratio and bolometric temperature) obtained fromHerschelobservations. It seeks to assess whether the cores evolve in number and mass in tandem with their host clumps and to determine the possible factors influencing the formation of massive cores (M> 24 M_⊙). Methods. We analyzed the masses of 6348 fragments, estimated from 1.4 mm continuum data for 1007 ALMAGAL clumps. Leveraging this unprecedentedly large dataset, we evaluated statistical relationships between clump parameters, estimated over ~0.1 pc scales, and fragment properties, corresponding to scales of a few thousand astronomical units, while accounting for potential biases related to distance and observational resolution. Our results were further compared with predictions from numerical simulations. Results. The fragmentation level correlates preferentially with clump surface density, supporting a scenario of density-driven fragmentation; however, it does not show any clear dependence on total clump mass. Both the mass of the most massive core and the core formation efficiency exhibit a broad range and increase, on average, by an order of magnitude across intervals defined by evolutionary indicators such as clump-dust temperature and the luminosity-to-mass ratio. This suggests that core growth continues throughout clump evolution, favoring clump-fed over core-fed theoretical scenarios. However, significant scatter in these relationships indicates that multiple factors, including magnetic fields, turbulence, and stellar feedback, not quantifiable with continuum data, influence fragmentation, as also suggested by comparison with numerical simulations. 

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2. ALMAGAL: III. Compact source catalog: Fragmentation statistics and physical evolution of the core population

   https://doi.org/10.1051/0004-6361/202452706  

   Coletta, A; Molinari, S; Schisano, E; Traficante, A; Elia, D; Benedettini, M; Mininni, C; Soler, J D; Sánchez-Monge, Á; Schilke, P; et al (April 2025, Astronomy & Astrophysics)

   The physical mechanisms behind the fragmentation of high-mass dense clumps into compact star-forming cores and the properties of these cores are fundamental topics that are heavily investigated in current astrophysical research. The ALMAGAL survey provides the opportunity to study this process at an unprecedented level of detail and statistical significance, featuring high-angular resolution 1.38 mm ALMA observations of 1013 massive dense clumps at various Galactic locations. These clumps cover a wide range of distances (~2–8 kpc), masses (~10²–10⁴M_⊙), surface densities (0.1–10 g cm⁻²), and evolutionary stages (luminosity over mass ratio indicator of ~0.05 <L/M <450L_⊙/M_⊙). Here, we present the catalog of compact sources obtained with theCuTExalgorithm from continuum images of the full ALMAGAL clump sample combining ACA-7 m and 12 m ALMA arrays, reaching a uniform high median spatial resolution of ~1400 au (down to ~800 au). We characterize and discuss the revealed fragmentation properties and the photometric and estimated physical parameters of the core population. The ALMAGAL compact source catalog includes 6348 cores detected in 844 clumps (83% of the total), with a number of cores per clump between 1 and 49 (median of 5). The estimated core diameters are mostly within ~800–3000 au (median of 1700 au). We assigned core temperatures based on theL/Mof the hosting clump, and obtained core masses from 0.002 to 345M_⊙(complete above 0.23 M_⊙), exhibiting a good correlation with the core radii (M ∝ R^2.6). We evaluated the variation in the core mass function (CMF) with evolution as traced by the clumpL/M, finding a clear, robust shift and change in slope among CMFs within subsamples at different stages. This finding suggests that the CMF shape is not constant throughout the star formation process, but rather it builds (and flattens) with evolution, with higher core masses reached at later stages. We found that all cores within a clump grow in mass on average with evolution, while a population of possibly newly formed lower-mass cores is present throughout. The number of cores increases with the core masses, at least until the most massive core reaches ~10M_⊙. More generally, our results favor a clump-fed scenario for high-mass star formation, in which cores form as low-mass seeds, and then gain mass while further fragmentation occurs in the clump. 

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3. ALMAGAL: I. The ALMA evolutionary study of high-mass protocluster formation in the Galaxy: Presentation of the survey and early results

   https://doi.org/10.1051/0004-6361/202452702  

   Molinari, S; Schilke, P; Battersby, C; Ho, P_T P; Sánchez-Monge, Á; Traficante, A; Jones, B; Beltrán, M T; Beuther, H; Fuller, G A; et al (April 2025, Astronomy & Astrophysics)

   Context. A large fraction of stars form in clusters containing high-mass stars, which subsequently influences the local and galaxy-wide environment. Aims. Fundamental questions about the physics responsible for fragmenting molecular parsec-scale clumps into cores of a few thousand astronomical units (au) are still open, that only a statistically significant investigation with ALMA is able to address; for instance: the identification of the dominant agents that determine the core demographics, mass, and spatial distribution as a function of the physical properties of the hosting clumps, their evolutionary stage and the different Galactic environments in which they reside. The extent to which fragmentation is driven by clumps dynamics or mass transport in filaments also remains elusive. Methods. With the ALMAGAL project, we observed the 1.38 mm continuum and lines toward more than 1000 dense clumps in our Galaxy, withM≥ 500 M_⊙, Σ ≥ 0.1 g cm⁻²andd≤ 7.5 kiloparsec (kpc). Two different combinations of ALMA Compact Array (ACA) and 12-m array setups were used to deliver a minimum resolution of ∼1000 au over the entire sample distance range. The sample covers all evolutionary stages from infrared dark clouds (IRDCs) to H IIregions from the tip of the Galactic bar to the outskirts of the Galaxy. With a continuum sensitivity of 0.1 mJy, ALMAGAL enables a complete study of the clump-to-core fragmentation process down toM∼ 0.3 M_⊙across the Galaxy. The spectral setup includes several molecular lines to trace the multiscale physics and dynamics of gas, notably CH₃CN, H₂CO, SiO, CH₃OH, DCN, HC₃N, and SO, among others. Results. We present an initial overview of the observations and the early science product and results produced in the ALMAGAL Consortium, with a first characterization of the morphological properties of the continuum emission detected above 5σin our fields. We used “perimeter-versus-area” and convex hull-versus-area metrics to classify the different morphologies. We find that more extended and morphologically complex (significantly departing from circular or generally convex) shapes are found toward clumps that are relatively more evolved and have higher surface densities. Conclusions. ALMAGAL is poised to serve as a game-changer for a number of specific issues in star formation: clump-to-core fragmentation processes, demographics of cores, core and clump gas chemistry and dynamics, infall and outflow dynamics, and disk detections. Many of these issues will be covered in the first generation of papers that closely follow on the present publication. 

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4. ALMAGAL. VII. Cataloging Hierarchical Continuum Structure from Cores to Clumps across the Galactic Disk

   https://doi.org/10.3847/1538-4357/ae2fec  

   Wallace, Jennifer; Kolz, Taevis; Battersby, Cara; Kuznetsova, Aleksandra; Sánchez-Monge, Álvaro; Schisano, Eugenio; Coletta, Alessandro; Zhang, Qizhou; Molinari, Sergio; Schilke, Peter; et al (February 2026, The Astrophysical Journal)

   Abstract Investigating the multiscale fragmentation of dense clumps into compact cores is essential for understanding the processes that govern the initial distribution of mass in stellar clusters and how high-mass stars (>8M_⊙) form. We present a catalog of the hierarchical continuum structure from 904 clumps observed in the ALMAGAL program, a high-resolution (0 $\stackrel{\text{″}}{.}$ 15–0 $\stackrel{\text{″}}{.}$ 8) 1.38 mm Atacama Large Millimeter/submillimeter Array large program targeting dense clumps capable of high-mass star formation throughout the Galactic disk. We useastrodendro, a dendrogram-based algorithm, on a uniform linear resolution (2000 au) version of the data to extract 5160 continuum structures with effective radii spanning 800–42000 au and estimated masses between 0.05–670M_⊙. With our large sample, we statistically examine differences in clump properties for regions with varying levels of hierarchical complexity. We find that clumps exhibiting the richest hierarchical morphology have distributions with higher dust temperatures, surface densities, luminosity-to-mass (L/M) ratios, and most massive core masses, indicating that these regions tend to be at later evolutionary stages. We find a positive correlation between the mass of cores from the ALMAGAL core catalog and the surface density of their surrounding structures identified in this work. However, this correlation is weaker for cores in more evolved clumps, where lower-mass cores can be found at higher local surface densities. This could indicate that some cores accrete mass less efficiently from the intraclump reservoir than others, despite the total available mass increasing over time, a scenario that is congruent with a clump-fed core accretion model. 

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5. SIEGE: IV. Compact star clusters in cosmological simulations with a high star formation efficiency and subparsec resolution

   https://doi.org/10.1051/0004-6361/202453252  

   Pascale, R; Calura, F; Vesperini, E; Rosdahl, J; Nipoti, C; Giunchi, E; Lacchin, E; Lupi, A; Messa, M; Meneghetti, M; et al (July 2025, Astronomy & Astrophysics)

   The formation of compact high-redshift star-forming clumps, along with the physical processes driving their evolution and their potential connection to present-day globular clusters (GCs), are key open questions in studies of galaxy formation. In this work, we aim to shed light on these aspects using the SImulating the Environment where Globular clusters Emerged (SIEGE) project, a suite of cosmological zoom-in simulations with subparsec resolution that is specifically designed to investigate the physical conditions behind the origin of compact stellar systems in high-redshift environments. The simulations analyzed in this study are focused on a dwarf galaxy with a virial mass of a few 10⁹M_⊙atz= 6.14, where the spatial resolution reaches 0.3 pc h⁻¹. Individual stars are formed directly by sampling the initial mass function, with a 100% star formation efficiency. This setup is designed to explore the impact of a high star formation efficiency under high-redshift conditions. The simulation reveals the emergence of numerous stellar clumps with sizes of 1–3 pc, stellar surface densities up to almost 10⁴M_⊙pc⁻², and masses predominantly spanning 10³M_⊙to several 10⁴M_⊙, with a few reaching 10⁵M_⊙and up to 10⁶M_⊙. All clumps form during intense, short bursts of star formation lasting less than a megayear, without noticeable signs of second peaks of star formation or accretion, often with negligible dark matter content (i.e., dark-to-stellar mass ratios below 1 within three times their effective radii). We measured a clear correlation between mass and size, with a clump mass function described by a power law with a slope of −2. Star formation conditions in the simulation reveal a behaviour that is similar to that of a feedback-free starburst scenario, where dense clumps form due to inefficient stellar feedback over small timescales. Notably, some clumps exhibit properties that closely resemble those of present-day globular clusters, highlighting their potential evolutionary connection. 

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