EPoS Contribution

Investigating massive star formation with ALMAGAL: fragmentation of dense clumps, compact source catalog and physical analysis of the core population Alessandro Coletta INAF-IAPS, Rome, IT
The physical mechanisms behind high-mass star formation, and in particular the fragmentation of massive dense clumps into compact star-forming cores (and their properties) are fundamental topics heavily investigated in current astrophysical research. The ALMAGAL survey provides the opportunity to study these processes with an unprecedented level of statistical and physical significance and detail, featuring high-resolution 1.4 mm ALMA observations of 1000+ massive dense clumps at various Galactic locations, which cover a wide range of distances (∼ 2 - 8 kpc), masses (10² - 10⁴ M_⊙), surface densities (0.1 − 10 g cm^-2), and evolutionary stages (∼ 0.05 < L/M < 500 L_⊙/M_⊙), achieving a uniformly high spatial resolution of ≲ 1000 AU, able to access the typical core scales. In this contribution I will present the first scientific analysis of the ALMAGAL data, aiming at investigating the clump fragmentation process by statistically and physically characterizing its outcome, in order to get indications on mechanisms and evolution of the massive star formation process and formulate a likely coherent scenario. After an extensive work of tests and tuning, an optimized source detection and photometry procedure, employing an implemented version of the CuTEx algorithm, was applied on the continuum maps of the whole ALMAGAL clump sample to extract the catalog of ALMAGAL compact sources (cores). The catalog includes 6303 cores detected in 838 clumps (83% of the total), with a number of detections per clump between 1 and 49 (median of 5). The photometric properties of the detected compact sources were characterized and their main physical parameters estimated, finding core sizes within ∼ 1000 − 3000 AU (median of 1700 AU), and masses from ∼ 0.01 to ∼ 300 M_⊙, with the two parameters showing a good correlation and a power-law relation M ∝ R^2.6. The shape of the observed Core Mass Function (CMF) was analyzed by fitting a power law to the high-mass tail, finding that only for masses ≥ 3 M_⊙ the shape of the distribution is well reproduced by a power law (with slopes slightly steeper than Salpeter’s −1.35). We evaluated the variation of the CMF as a function of evolution, as traced by the clump evolutionary indicator L/M, finding a clear shift among CMFs within subsamples at different stages, with more massive cores appearing at later stages, thus suggesting that the CMF shape is not constant throughout the star formation process but rather builds with evolution. We then investigated the relations among the revealed fragmentation properties, the physical parameters of the cores, and the properties of the hosting clumps (also comparing with results from numerical simulations), finding that both the core masses and the number of fragments increase on average with evolution and the surface density of the clump, which leads to an increasing Core Formation Efficiency (CFE). A population of low-mass cores at nearly constant mass of ∼ 0.2 M_⊙ is nonetheless revealed at all stages, possibly corresponding to the newly formed fragments. Overall, our results suggest a likely gravity-driven clump-fed scenario for high-mass star formation, with cores gradually accreting mass from the intraclump medium in a competitive way in the context of a dynamical, multi-scale framework, while clump fragmentation proceeds in parallel throughout evolution.

Caption: Distribution of the number of fragments detected across the ALMAGAL clump sample, showing a wide range of fragmentation degrees (left). Additional statistics are also given. Estimated core formation efficiency (CFE) as a function of the clump L/M evolutionary indicator, color-coded by the clump average surface density (right). Median values of CFE within given bins of L/M are shown in black.
Collaborators: S. Molinari, INAF-IAPS, IT E. Schisano, INAF-IAPS, IT A. Traficante, INAF-IAPS, IT INAF-IAPS SF Group ALMAGAL Team	Relevant topic(s): Cores Fragmentation High-Mass SF
Relevant Big Question: Which are the physical forces/processes that dominate massive clump fragmentation and its outcome?