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Recent high-angular-resolution observations indicate the need for core growth to form high-mass stars. To understand the gas dynamics at the core scale in the very early evolutionary stages before being severely affected by feedback, we have conducted Atacama Large Millimeter/submillimeter Array (ALMA) observations toward a 70 μ m dark massive clump, G337.541-00.082 as part of the Global and Local infall in the ASHES sample (GLASHES) program. Using dense gas tracers such as N _2 H ^+ ( J = 1–0) and HNC ( J = 3–2), we find signs of infall from the position–velocity diagram and more directly from the blue asymmetry profile in addition to the clump-scale velocity gradient. We estimate infall velocities from intermediate and low-mass cores to be 0.28–1.45 km s ^−1 , and infall rates to be on the order of 10 ^−4 –10 ^−3 M _⊙ yr ^−1 , both are higher than those measured in low-mass star-forming regions by more than a factor of 5 and an order of magnitude, respectively. We find a strong correlation between the infall velocity with the nonthermal velocity dispersion, suggesting that infall may contribute significantly to the observed line width. Consistent with clump-fed scenarios, we show that the mass infall rate is larger for larger core masses and shorter distances to the clump center. Such high infall rates in cores embedded in IRDCs can be considered as strong signs of core growth, allowing high-mass star formation from intermediate-mass cores that would not initially form high-mass stars at their current mass.

Only a handful of massive starless core candidates have been discovered so far, but none of them have been fully confirmed. Within the MM1 clump in the filamentary infrared dark cloud G34.43+0.24 that was covered by the Atacama Large Millimeter/submillimeter Array (ALMA) ATOMS survey at Band 3 (∼2″, 6000 au) and the ALMA-QUARKS survey at Band 6 (∼0.″3, 900 au), two prestellar core candidates MM1-C and E1 with masses of 71 and 20 M _⊙ and radii of 2100–4400 au were discovered. The two cores show no obvious sign of star formation activities. In particular, MM1-C is a very promising massive prestellar core candidate with a total gas mass of 71 M _⊙ . Within MM1-C, we detected two extremely dense substructures, C1 and C2, as characterized by their high densities of ${n}_{{{\rm{H}}}_{2}}\sim {10}^{8\mbox{--}9}\,{\mathrm{cm}}^{-3}$ . Moreover, evidence of further fragmentation in C2 was also revealed. We have detected the primordial fragmentation in the earliest stage of massive star formation, and we speculate that MM1-C would be the birthplace of a massive multiple system. However, we cannot fully rule out the possibility that the massive prestellar core MM1-C will just form a cluster of low-mass stars if it undergoes further fragmentation.

High-latitude (∣ b ∣ > 30°) molecular clouds have virial parameters that exceed 1, but whether these clouds can form stars has not been studied systematically. Using JCMT SCUBA-2 archival data, we surveyed 70 fields that target high-latitude Planck Galactic cold clumps (HLPCs) to find dense cores with density of 10 ^5 –10 ^6 cm ^−3 and size of 1 × 10 ^21 cm ^−2 ). At an average rms of 15 mJy beam ^−1 , we detected Galactic dense cores in only one field, G6.04+36.77 (L183) while also identifying 12 extragalactic objects and two young stellar objects. Compared to the low-latitude clumps, dense cores are scarce in HLPCs. With synthetic observations, the densities of cores are constrained to be n _c ≲ 10 ^5 cm ^−3 should they exist in HLPCs. Low-latitude clumps, Taurus clumps, and HLPCs form a sequence where a higher virial parameter corresponds to a lower dense-core detection rate. If HLPCs were affected by the Local Bubble, the scarcity should favor turbulence-inhibited rather than supernova-driven star formation. Studies of the formation mechanism of the L183 molecular cloud are warranted.

Using new continuum and molecular line data from the Atacama Large Millimeter/submillimeter Array Three-millimeter Observations of Massive Star-forming Regions (ATOMS) survey and archival Very Large Array, 4.86 GHz data, we present direct observational evidence of hierarchical triggering relating three epochs of massive star formation in a ringlike H ii region, G24.47+0.49. We find from radio flux analysis that it is excited by a massive star(s) of spectral type O8.5V–O8V from the first epoch of star formation. The swept-up ionized ring structure shows evidence of secondary collapse, and within this ring, a burst of massive star formation is observed in different evolutionary phases, which constitutes the second epoch. ATOMS spectral line (e.g., HCO ^+ (1–0)) observations reveal an outer concentric molecular gas ring expanding at a velocity of ∼9 km s ^−1 , constituting the direct and unambiguous detection of an expanding molecular ring. It harbors twelve dense molecular cores with surface mass density greater than 0.05 g cm ^−2 , a threshold typical of massive star formation. Half of them are found to be subvirial and thus in gravitational collapse making them the third epoch of potential massive star-forming sites.

In this paper, we present a detailed analysis of the IRS 17 filament within the intermediate-mass protocluster IRAS 08448-4343 (of ∼10 ^3 L _⊙ ), using ALMA data from the ATOMS 3 mm and QUARKS 1.3 mm surveys. The IRS 17 filament, which spans ∼54,000 au (0.26 pc) in length and ∼4000 au (0.02 pc) in width, exhibits a complex, multicomponent velocity field and harbors hierarchical substructures. These substructures include three bundles of seven velocity-coherent fibers and 29 dense ( n ∼ 10 ^8 cm ^−3 ) condensations. The fibers have a median length of ∼4500 au and a median width of ∼1400 au. Among these fibers, four are identified as “fertile,” each hosting at least three dense condensations, which are regarded as the “seeds” of star formation. While the detected cores are randomly spaced within the IRS 17 filament based on the 3 mm dust continuum image, periodic spacing (∼1600 au) of condensations is observed in the fertile fibers according to the 1.3 mm dust map, consistent with the predictions of linear isothermal cylinder fragmentation models. These findings underscore the crucial role of fibers in star formation and suggest a hierarchical fragmentation process that extends from the filament to the fibers and, ultimately, to the smallest-scale condensations.

We study the astrochemical diagnostics of the isolated massive protostar G28.20-0.05. We analyze data from Atacama Large Millimeter/submillimeter Array 1.3 mm observations with a resolution of 0.″2 (∼1000 au). We detect emission from a wealth of species, including oxygen-bearing (e.g., H _2 CO, CH _3 OH, CH _3 OCH _3 ), sulfur-bearing (SO _2 , H _2 S), and nitrogen-bearing (e.g., HNCO, NH _2 CHO, C _2 H _3 CN, C _2 H _5 CN) molecules. We discuss their spatial distributions, physical conditions, correlation between different species, and possible chemical origins. In the central region near the protostar, we identify three hot molecular cores (HMCs). HMC1 is part of a millimeter continuum ring-like structure, is closest in projection to the protostar, has the highest temperature of ∼300 K, and shows the most line-rich spectra. HMC2 is on the other side of the ring, has a temperature of ∼250 K, and is of intermediate chemical complexity. HMC3 is further away, ∼3000 au in projection, cooler (∼70 K), and is the least line-rich. The three HMCs have similar mass surface densities (∼10 g cm ^−2 ), number densities ( n _H ∼ 10 ^9 cm ^−3 ), and masses of a few solar masses. The total gas mass in the cores and in the region out to 3000 au is ∼25 M _⊙ , which is comparable to that of the central protostar. Based on spatial distributions of peak line intensities as a function of excitation energy, we infer that the HMCs are externally heated by the protostar. We estimate column densities and abundances of the detected species and discuss the implications for hot core astrochemistry.

We report high angular resolution observations, made with the Atacama Large Millimeter Array in band 6, of high excitation molecular lines of ${\mathrm{CH}}_{3}\mathrm{CN}$ and SO _2 and of the H29 α radio recombination line toward the G345.0061+01.794 B HC H ii region in order to investigate the physical and kinematical characteristics of its surroundings. Emission was detected in all observed components of the J = 14 →13 rotational ladder of ${\mathrm{CH}}_{3}\mathrm{CN}$ and in the 30 _4,26 –30 _3,27 , and 32 _4,28 –32 _3,29 lines of SO _2 . The peak of the velocity-integrated molecular emission is located ∼0.″4 northwest of the peak of the continuum emission. The first-order moment images and channel maps show a velocity gradient of 1.1 km s ^−1 arcsec ^−1 across the source and a distinctive spot of blueshifted emission toward the peak of the zero-order moment. The rotational temperature is found to decrease from 252±24 K at the peak position to 166±16 K at its edge, indicating that our molecular observations are probing a hot molecular core that is internally excited. The emission in the H29 α line arises from a region of 0.″65 in size, where its peak coincides with that of the dust continuum. We model the kinematical characteristics of the “central blue spot” feature as due to infalling motions, suggesting a central mass of 172.8±8.8 M _⊙ . Our observations indicate that this HC H ii region is surrounded by a compact structure of hot molecular gas, which is rotating and infalling toward a central mass, that is most likely confining the ionized region. The observed scenario is reminiscent of a “butterfly pattern” with an approximately edge-on torus and ionized gas roughly parallel to its rotation axis.

There is growing evidence that high-mass star formation and hub-filament systems (HFS) are intricately linked. The gas kinematics along the filaments and the forming high-mass star(s) in the central hub are in excellent agreement with the new generation of global hierarchical high-mass star formation models. In this paper, we present an observational investigation of a typical HFS cloud, G310.142+0.758 (G310 hereafter), which reveals unambiguous evidence of mass inflow from the cloud scale via the filaments onto the forming protostar(s) at the hub conforming with the model predictions. Continuum and molecular line data from the ATOMS and MALT90 surveys that cover different spatial scales are used. Three filaments (with a total mass of 5.7 ± 1.1 × 10 ^3 M _⊙ ) are identified converging toward the central hub region where several signposts of high-mass star formation have been observed. The hub region contains a massive clump (1280 ± 260 M _⊙ ) harboring a central massive core. Additionally, five outflow lobes are associated with the central massive core implying a forming cluster. The observed large-scale, smooth, and coherent velocity gradients from the cloud down to the core scale, and the signatures of infall motion seen in the central massive clump and core, clearly unveil a nearly continuous, multi-scale mass accretion/transfer process at a similar mass infall rate of ∼10 ^−3 M _⊙ yr ^−1 over all scales, feeding the central forming high-mass protostar(s) in the G310 HFS cloud.

The initial conditions found in infrared dark clouds (IRDCs) provide insights on how high-mass stars and stellar clusters form. We have conducted high-angular resolution and high-sensitivity observations toward thirty-nine massive IRDC clumps, which have been mosaicked using the 12 and 7 m arrays from the Atacama Large Millimeter/submillimeter Array. The targets are 70 μ m dark massive (220–4900 M _⊙ ), dense (>10 ^4 cm ^−3 ), and cold (∼10–20 K) clumps located at distances between 2 and 6 kpc. We identify an unprecedented number of 839 cores, with masses between 0.05 and 81 M _⊙ using 1.3 mm dust continuum emission. About 55% of the cores are low-mass (

The Atacama Large Millimeter/submillimeter Array (ALMA) Survey of Star Formation and Evolution in Massive Protoclusters with Blue Profiles (ASSEMBLE) aims to investigate the process of mass assembly and its connection to high-mass star formation theories in protoclusters in a dynamic view. We observed 11 massive ( M _clump ≳ 10 ^3 M _⊙ ), luminous ( L _bol ≳ 10 ^4 L _⊙ ), and blue-profile (infall signature) clumps by ALMA with resolution of ∼2200–5500 au (median value of 3500 au) at 350 GHz (870 μ m). We identified 248 dense cores, including 106 cores showing protostellar signatures and 142 prestellar core candidates. Compared to early stage infrared dark clouds (IRDCs) by ASHES, the core mass and surface density within the ASSEMBLE clumps exhibited a significant increment, suggesting concurrent core accretion during the evolution of the clumps. The maximum mass of prestellar cores was found to be 2 times larger than that in IRDCs, indicating that evolved protoclusters have the potential to harbor massive prestellar cores. The mass relation between clumps and their most massive core (MMCs) is observed in ASSEMBLE but not in IRDCs, which is suggested to be regulated by multiscale mass accretion. The mass correlation between the core clusters and their MMCs has a steeper slope compared to that observed in stellar clusters, which can be due to fragmentation of the MMC and stellar multiplicity. We observe a decrease in core separation and an increase in central concentration as protoclusters evolve. We confirm primordial mass segregation in the ASSEMBLE protoclusters, possibly resulting from gravitational concentration and/or gas accretion.