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Context. The study of molecular line emission is crucial to unveil the kinematics and the physical conditions of gas in star-forming regions. We use data from the ALMAGAL survey, which provides an unprecedentedly large statistical sample of high-mass star-forming clumps that helps us to remove bias and reduce noise (e.g., due to source peculiarities, selection, or environmental effects) to determine how well individual molecular species trace continuum emission. Aims. Our aim is to quantify whether individual molecular transitions can be used reliably to derive the physical properties of the bulk of the H₂gas, by considering morphological correlations in their overall integrated molecular line emission with the cold dust. We selected transitions of H₂CO, CH₃OH, DCN, HC₃N, CH₃CN, CH₃OCHO, SO, and SiO and compared them with the 1.38 mm dust continuum emission at different spatial scales in the ALMAGAL sample. We included two transitions of H₂CO to understand whether the validity of the results depends on the excitation condition of the selected transition of a molecular species. The ALMAGAL project observed more than 1000 candidate high-mass star-forming clumps in ALMA band 6 at a spatial resolution down to 1000 au. We analyzed a total of 1013 targets that cover all evolutionary stages of the high-mass star formation process and different conditions of clump fragmentation. Methods. For the first time, we used the method called histogram of oriented gradients (HOG) as implemented in the toolastroHOGon a large statistical sample to compare the morphology of integrated line emission with maps of the 1.38 mm dust continuum emission. For each clump, we defined two masks: the first mask covered the extended more diffuse continuum emission, and the second smaller mask that only contained the compact sources. We selected these two masks to study whether and how the correlation among the selected molecules changes with the spatial scale of the emission, from extended more diffuse gas in the clumps to denser gas in compact fragments (cores). Moreover, we calculated the Spearman correlation coefficient and compared it with our astroHOG results. Results. Only H₂CO, CH₃OH, and SO of the molecular species we analyzed show emission on spatial scales that are comparable with the diffuse 1.38 mm dust continuum emission. However, according the HOG method, the median correlation of the emission of each of these species with the continuum is only ~24–29%. In comparison with the dusty dense fragments, these molecular species still have low correlation values that are below 45% on average. The weak morphological correlation suggests that these molecular lines likely trace the clump medium or outer layers around dense fragments on average (in some cases, this might be due to optical depth effects) or also trace the inner parts of outflows at this scale. On the other hand DCN, HC₃N, CH₃CN₃and CH₃OCHO are well correlated with the dense dust fragments at above 60%. The lowest correlation is seen with SiO for the extended continuum emission and for compact sources. Moreover, unlike other outflow tracers, in a large fraction of the sources, SiO does not cover the area of the extended continuum emission well. This and the results of the astroHOG analysis reveal that SiO and SO do not trace the same gas, in contrast to what was previously thought. From the comparison of the results of the HOG method and the Spearman correlation coefficient, the HOG method gives much more reliable results than the intensity-based coefficient when the level of similarity of the emission morphology is estimated. 

The ALMA-IMF Large Program provides multi-tracer observations of 15 Galactic massive protoclusters at a matched sensitivity and spatial resolution. We focus on the dense gas kinematics of the G353.41 protocluster traced by N₂H⁺(1−0), with a spatial resolution of ~0.02 pc. G353.41, at a distance of ~2kpc, is embedded in a larger-scale (~8 pc) filament and has a mass of ~2.5 × 10³M_⊙within 1.3 × 1.3 pc². We extracted the N₂H⁺(1−0) isolated line component and decomposed it by fitting up to three Gaussian velocity components. This allows us to identify velocity structures that are either muddled or impossible to identify in the traditional position-velocity diagram. We identify multiple velocity gradients on large (~1 pc) and small scales (~0.2pc). We find good agreement between the N₂H⁺velocities and the previously reported DCN core velocities, suggesting that cores are kinematically coupled with the dense gas in which they form. We have measured nine converging “V-shaped” velocity gradients (VGs) (~20 km s⁻¹pc⁻¹) that are well resolved (sizes ~0.1 pc), mostly located in filaments, which are sometimes associated with cores near their point of convergence. We interpret these V-shapes as inflowing gas feeding the regions near cores (the immediate sites of star formation). We estimated the timescales associated with V-shapes as VG⁻¹, and we interpret them as inflow timescales. The average inflow timescale is ~67 kyr, or about twice the free-fall time of cores in the same area (~33 kyr) but substantially shorter than protostar lifetime estimates (~0.5 Myr). We derived mass accretion rates in the range of (0.35–8.77) × 10⁻⁴M_⊙yr⁻¹. This feeding might lead to further filament collapse and the formation of new cores. We suggest that the protocluster is collapsing on large scales, but the velocity signature of collapse is slow compared to pure free-fall. Thus, these data are consistent with a comparatively slow global protocluster contraction under gravity, and faster core formation within, suggesting the formation of multiple generations of stars over the protocluster’s lifetime. 

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. 

Context.Stars form preferentially in clusters embedded inside massive molecular clouds, many of which contain high-mass stars. Thus, a comprehensive understanding of star formation requires a robust and statistically well-constrained characterization of the formation and early evolution of these high-mass star clusters. To achieve this, we designed the ALMAGAL Large Program that observed 1017 high-mass star-forming regions distributed throughout the Galaxy, sampling different evolutionary stages and environmental conditions. Aims.In this work, we present the acquisition and processing of the ALMAGAL data. The main goal is to set up a robust pipeline that generates science-ready products, that is, continuum and spectral cubes for each ALMAGAL field, with a good and uniform quality across the whole sample. Methods.ALMAGAL observations were performed with the Atacama Large Millimeter/submillimeter Array (ALMA). Each field was observed in three different telescope arrays, being sensitive to spatial scales ranging from ≈1000 au up to ≈0.1 pc. The spectral setup allows sensitive (≈0.1 mJy beam⁻¹) imaging of the continuum emission at 219 GHz (or 1.38 mm), and it covers multiple molecular spectral lines observed in four different spectral windows that span about ≈4 GHz in frequency coverage. We have designed a Python-based processing workflow to calibrate and image these observational data. This ALMAGAL pipeline includes an improved continuum determination, suited for line-rich sources; an automatic self-calibration process that reduces phase-noise fluctuations and improves the dynamical range by up to a factor ≈5 in about 15% of the fields; and the combination of data from different telescope arrays to produce science-ready, fully combined images. Results.The final products are a set of uniformly generated continuum images and spectral cubes for each ALMAGAL field, including individual-array and combined-array products. The fully combined products have spatial resolutions in the range 800–2000 au, and mass sensitivities in the range 0.02–0.07M_⊙. We also present a first analysis of the spectral line information included in the ALMAGAL setup, and its potential for future scientific studies. As an example, specific spectral lines (e.g., SiO and CH₃CN) at ≈1000 au scales resolve the presence of multiple outflows in clusters and will help us to search for disk candidates around massive protostars. Moreover, the broad frequency bands provide information on the chemical richness of the different cluster members, which can be used to study the chemical evolution during the formation process of star clusters. 

The stellar initial mass function (IMF) is critical to our understanding of star formation and the effects of young stars on their environment. On large scales, it enables us to use tracers such as UV or Hα emission to estimate the star formation rate of a system and interpret unresolved star clusters across the Universe. So far, there is little firm evidence of large-scale variations of the IMF, which is thus generally considered “universal”. Stars form from cores, and it is now possible to estimate core masses and compare the core mass function (CMF) with the IMF, which it presumably produces. The goal of the ALMA-IMF large programme is to measure the core mass function at high linear resolution (2700 au) in 15 typical Milky Way protoclusters spanning a mass range of 2.5 × 10³to 32.7 × 10³M_⊙. In this work, we used two different core extraction algorithms to extract ≈680 gravitationally bound cores from these 15 protoclusters. We adopted a per core temperature using the temperature estimate from the point-process mapping Bayesian method (PPMAP). A power-law fit to the CMF of the sub-sample of cores above the 1.64M_⊙completeness limit (330 cores) through the maximum likelihood estimate technique yields a slope of 1.97 ± 0.06, which is significantly flatter than the 2.35 Salpeter slope. Assuming a self-similar mapping between the CMF and the IMF, this result implies that these 15 high-mass protoclusters will generate atypical IMFs. This sample currently is the largest sample that was produced and analysed self-consistently, derived at matched physical resolution, with per core temperature estimates, and cores as massive as 150M_⊙. We provide both the raw source extraction catalogues and the catalogues listing the source size, temperature, mass, spectral indices, and so on in the 15 protoclusters. 

Context.The star formation process leads to an increased chemical complexity in the interstellar medium. Sites associated with high-mass star and cluster formation exhibit a so-called hot core phase, characterized by high temperatures and column densities of complex organic molecules. Aims.We aim to systematically search for and identify a sample of hot cores toward the 15 Galactic protoclusters of the ALMA-IMF Large Program and investigate their statistical properties. Methods.We built a comprehensive census of hot core candidates toward the ALMA-IMF protoclusters based on the detection of two CH₃OCHO emission lines at 216.1 GHz. We used the source extraction algorithm GExt2D to identify peaks of methyl formate (CH₃OCHO) emission, a complex species commonly observed toward sites of star formation. We performed a cross-matching with the catalog of thermal dust continuum sources from the ALMA-IMF 1.3 mm continuum data to infer their physical properties. Results.We built a catalog of 76 hot core candidates with masses ranging from ~0.2M_⊙to ~80M_⊙, of which 56 are new detections. A large majority of these objects, identified from methyl formate emission, are compact and rather circular, with deconvolved full width at half maximum (FWHM) sizes of ~2300 au on average. The central sources of two target fields show more extended, but still rather circular, methyl formate emission with deconvolved FWHM sizes of ~6700 au and 13 400 au. About 30% of our sample of methyl formate sources have core masses above 8M_⊙and range in size from ~1000 au to 13 400 au, which is in line with measurements of archetypical hot cores. The origin of the CH₃OCHO emission toward the lower-mass cores may be explained as a mixture of contributions from shocks or may correspond to objects in a more evolved state (i.e., beyond the hot core stage). We find that the fraction of hot core candidates increases with the core mass, suggesting that the brightest dust cores are all in the hot core phase. Conclusions.Our results suggest that most of these compact methyl formate sources are readily explained by simple symmetric models, while collective effects from radiative heating and shocks from compact protoclusters are needed to explain the observed extended CH₃OCHO emission. The large fraction of hot core candidates toward the most massive cores suggests that they rapidly enter the hot core phase and that feedback effects from the forming protostar(s) impact their environment on short timescales. 

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. 

Context. The origin of the stellar initial mass function (IMF) and its relation with the core mass function (CMF) are actively debated issues with important implications in astrophysics. Recent observations in the W43 molecular complex of top-heavy CMFs, with an excess of high-mass cores compared to the canonical mass distribution, raise questions about our understanding of the star formation processes and their evolution in space and time. Aims. We aim to compare populations of protostellar and prestellar cores in three regions imaged in the ALMA-IMF Large Program. Methods. We created an homogeneous core catalogue in W43, combining a new core extraction in W43-MM1 with the catalogue of W43-MM2&MM3 presented in a previous work. Our detailed search for protostellar outflows enabled us to identify between 23 and 30 protostellar cores out of 127 cores in W43-MM1 and between 42 and 51 protostellar cores out of 205 cores in W43-MM2&MM3. Cores with neither outflows nor hot core emission are classified as prestellar candidates. Results. We found a similar fraction of cores which are protostellar in the two regions, about 35%. This fraction strongly varies in mass, from f pro ≃ 15–20% at low mass, between 0.8 and 3 M ⊙ up to f pro ≃ 80% above 16 M ⊙ . Protostellar cores are found to be, on average, more massive and smaller in size than prestellar cores. Our analysis also revealed that the high-mass slope of the prestellar CMF in W43, α = -1.46 -0.19 +0.12 , is consistent with the Salpeter slope, and thus the top-heavy form measured for the global CMF, α = −0.96 ± 0.09, is due to the protostellar core population. Conclusions. Our results could be explained by ‘clump-fed’ models in which cores grow in mass, especially during the protostellar phase, through inflow from their environment. The difference between the slopes of the prestellar and protostellar CMFs moreover implies that high-mass cores grow more in mass than low-mass cores. 

Context.Hot cores are signposts of the protostellar activity of dense cores in star-forming regions. W43-MM1 is a young region that is very rich in terms of high-mass star formation, which is highlighted by the presence of large numbers of high-mass cores and outflows. Aims.We aim to systematically identify the massive cores in W43-MM1 that contain a hot core and compare their molecular composition. Methods.We used Atacama Large Millimeter/sub-millimeter Array (ALMA) high-spatial resolution (~2500 au) data to identify line-rich protostellar cores and carried out a comparative study of their temperature and molecular composition. Here, the identification of hot cores is based on both the spatial distribution of the complex organic molecules and the contribution of molecular lines relative to the continuum intensity. We rely on the analysis of CH₃CN and CH₃CCH to estimate the temperatures of the selected cores. Finally, we rescale the spectra of the different hot cores based on their CH₃OCHO line intensities to directly compare the detections and line intensities of the other species. Results.W43-MM1 turns out to be a region that is rich in massive hot cores. It contains at least one less massive (core #11, 2M_⊙) and seven massive (16−100M_⊙) hot cores. The excitation temperature of CH₃CN, whose emission is centred on the cores, is of the same order for all of them (120–160 K). There is a factor of up to 30 difference in the intensity of the lines of complex organic molecules (COMs). However the molecular emission of the hot cores appears to be the same or within a factor of 2–3. This suggests that these massive cores, which span about an order of magnitude in core mass, have a similar chemical composition and show similar excitation of most of the COMs. In contrast, CH₃CCH emission is found to preferentially trace the envelope, with a temperature ranging from 50 K to 90 K. Lines in core #11 are less optically thick, which makes them proportionally more intense compared to the continuum than lines observed in the more massive hot cores. Core #1, the most massive hot core of W43-MM1, shows a richer line spectrum than the other cores in our sample, in particular in N-bearing molecules and ethylene glycol lines. In core #2, the emission of O-bearing molecules, such as OCS, CH₃OCHO, and CH₃OH, does not peak at the dust continuum core centre; the blueshifted and redshifted emission corresponds to the outflow lobes, suggesting formation via sublimation of the ice mantles through shocks or UV irradiation on the walls of the cavity. These data establish a benchmark for the study of other massive star-formation regions and hot cores. 

Context. Among the most central open questions regarding the initial mass function (IMF) of stars is the impact of environment on the shape of the core mass function (CMF) and thus potentially on the IMF. Aims. The ALMA-IMF Large Program aims to investigate the variations in the core distributions (CMF and mass segregation) with cloud characteristics, such as the density and kinematic of the gas, as diagnostic observables of the formation process and evolution of clouds. The present study focuses on the W43-MM2&MM3 mini-starburst, whose CMF has recently been found to be top-heavy with respect to the Salpeter slope of the canonical IMF. Methods. W43-MM2&MM3 is a useful test case for environmental studies because it harbors a rich cluster that contains a statistically significant number of cores (specifically, 205 cores), which was previously characterized in Paper III. We applied a multi-scale decomposition technique to the ALMA 1.3 mm and 3 mm continuum images of W43-MM2&MM3 to define six subregions, each 0.5–1 pc in size. For each subregion we characterized the probability distribution function of the high column density gas, η -PDF, using the 1.3 mm images. Using the core catalog, we investigate correlations between the CMF and cloud and core properties, such as the η -PDF and the core mass segregation. Results. We classify the W43-MM2&MM3 subregions into different stages of evolution, from quiescent to burst to post-burst, based on the surface number density of cores, number of outflows, and ultra-compact HII presence. The high-mass end (>1 M ⊙ ) of the subregion CMFs varies from close to the Salpeter slope (quiescent) to top-heavy (burst and post-burst). Moreover, the second tail of the η -PDF varies from steep (quiescent) to flat (burst and post-burst), as observed for high-mass star-forming clouds. We find that subregions with flat second η -PDF tails display top-heavy CMFs. Conclusions. In dynamical environments such as W43-MM2&MM3, the high-mass end of the CMF appears to be rooted in the cloud structure, which is at high column density and surrounds cores. This connection stems from the fact that cores and their immediate surroundings are both determined and shaped by the cloud formation process, the current evolutionary state of the cloud, and, more broadly, the star formation history. The CMF may evolve from Salpeter to top-heavy throughout the star formation process from the quiescent to the burst phase. This scenario raises the question of if the CMF might revert again to Salpeter as the cloud approaches the end of its star formation stage, a hypothesis that remains to be tested.