More Like this

1. ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions – I. Survey description and a first look at G9.62+0.19

   https://doi.org/10.1093/mnras/staa1577  

   Liu, Tie; Evans, Neal J; Kim, Kee-Tae; Goldsmith, Paul F; Liu, Sheng-Yuan; Zhang, Qizhou; Tatematsu, Ken’ichi; Wang, Ke; Juvela, Mika; Bronfman, Leonardo; et al (August 2020, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The ATOMS, standing for ALMA Three-millimeter Observations of Massive Star-forming regions, survey has observed 146 active star-forming regions with ALMA band 3, aiming to systematically investigate the spatial distribution of various dense gas tracers in a large sample of Galactic massive clumps, to study the roles of stellar feedback in star formation, and to characterize filamentary structures inside massive clumps. In this work, the observations, data analysis, and example science of the ATOMS survey are presented, using a case study for the G9.62+0.19 complex. Toward this source, some transitions, commonly assumed to trace dense gas, including CS J = 2−1, HCO+J = 1−0, and HCN J = 1−0, are found to show extended gas emission in low-density regions within the clump; less than 25 per cent of their emission is from dense cores. SO, CH3OH, H13CN, and HC3N show similar morphologies in their spatial distributions and reveal well the dense cores. Widespread narrow SiO emission is present (over ∼1 pc), which may be caused by slow shocks from large–scale colliding flows or H ii regions. Stellar feedback from an expanding H ii region has greatly reshaped the natal clump, significantly changed the spatial distribution of gas, and may also account for the sequential high-mass star formation in the G9.62+0.19 complex. The ATOMS survey data can be jointly analysed with other survey data, e.g. MALT90, Orion B, EMPIRE, ALMA_IMF, and ALMAGAL, to deepen our understandings of ‘dense gas’ star formation scaling relations and massive protocluster formation. 

   more » « less
2. 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. 

   more » « less
3. 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. 

   more » « less
4. The Rosetta Stone project: III. ALMA synthetic observations of fragmentation in high-mass star-forming clumps

   https://doi.org/10.1051/0004-6361/202554775  

   Nucara, Alice; Traficante, Alessio; Lebreuilly, Ugo; Tung, Ngo-Duy; Molinari, Sergio; Hennebelle, Patrick; Testi, Leonardo; Klessen, Ralf S; Pelkonen, Veli-Matti; Avison, Adam; et al (September 2025, Astronomy & Astrophysics)

   Context. The physical mechanisms that regulate the collapse of high-mass parsec-scale clumps and allow them to form clusters of new stars, including high-mass stars, represent a crucial aspect of star formation. Aims. To investigate these mechanisms, we developed the Rosetta Stone project: an end-to-end (simulations ⇔ observations) framework that is based on the systematic production of realistic synthetic observations of clump fragmentation and their subsequent comparison with real data. Methods. In this work, we compare ALMA 1.3 mm continuum dust emission observations from the Star formation in QUiescent And Luminous Objects (SQUALO) survey with a new set of 24 radiative magnetohydrodynamical (RMHD) simulations of high-mass clump fragmentation, post-processed using the CASA software to mimic the observing strategy of SQUALO (combining ACA and 12 m array). The simulations were initialized combining typical values of clump mass (500 and 1000 M_⊙) and radius (∼0.4 pc) with two levels of turbulence (Mach number,M, of 7 and 10) and three levels of magnetization (normalized mass-to-magnetic-flux ratio, µ, of ∼3, 10, and 100). Following the clump evolution over time with two initial random seeds projected along three orthogonal directions, we produced a collection of 732 synthetic fields. On each field, we performed source extraction and photometry using theHypersoftware, as in the SQUALO project, to quantitatively characterize how the initial conditions of the clump and the environment affect the observed fragmentation properties. Results. The synthetic observations of clump fragmentation at ∼7000 AU resolution revealed between 2 and 14 fragments per field, indicating a complex fragmentation process. Among the initial conditions of the simulations, magnetic fields have the largest impact on the fragment multiplicity at these scales. In advanced stages of clump evolution, a lower number of fragments is preferentially associated with magnetized clumps. The clump magnetization might also affect the clustering of fragments, favoring more tightly bound distributions when the magnetic field is stronger. Fragments identified at ∼7000 AU correspond to individual or multiple sink particles in ∼75% of the cases. This result suggests that not all identified fragments are actively forming stars. Both sink particles and fragments accrete mass throughout the whole clump evolution. This evidence favors a scenario in which fragments are not isolated from the environment and is thus consistent with results from the SQUALO survey. Conclusions. Our study demonstrates the importance of synthetic observations in interpreting results from interferometric observations. 

   more » « less
5. Fragmentation of the High-mass “Starless” Core G10.21-0.31: A Coherent Evolutionary Picture for Star Formation

   https://doi.org/10.3847/1538-4357/acb211  

   Jiao, Wenyu; Wang, Ke; Pillai, Thushara G.; Baug, Tapas; Zhang, Siju; Xu, Fengwei (March 2023, The Astrophysical Journal)

   Abstract G10.21-0.31 is a 70 μ m dark high-mass starless core ( M > 300 M ⊙ within r < 0.15 pc) identified in the Spitzer, Herschel, and APEX continuum surveys, and is believed to harbor the initial stages of high-mass star formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) and Submillimeter Array observations to resolve the internal structure of this promising high-mass starless core. Sensitive high-resolution ALMA 1.3 mm dust continuum emission reveals three cores of mass ranging within 11–18 M ⊙ , characterized by a turbulent fragmentation. Cores 1, 2, and 3 represent a coherent evolution of three different stages, characterized by outflows (CO and SiO), gas temperature (H 2 CO), and deuteration (N 2 D + /N 2 H + ). We confirm the potential for formation of high-mass stars in G10.21 and explore the evolution path of high-mass star formation. Yet, no high-mass prestellar core is present in G10.21. This suggests a dynamical star formation where cores grow in mass over time. 

   more » « less