How mass is accumulated from cloud-scale down to individual stars is a key open question in understanding highmass star formation. Here, we present the mass accumulation process in a hub-filament cloud G22 that is composed of four supercritical filaments. Velocity gradients detected along three filaments indicate that they are collapsing with a total mass infall rate of about 440 M e Myr −1 , suggesting the hub mass would be doubled in six free-fall times, adding up to ∼2 Myr. A fraction of the masses in the central clumps C1 and C2 can be accounted for through large-scale filamentary collapse. Ubiquitous blue profiles in HCO + (3-2) and 13 CO(3-2) spectra suggest a clump-scale collapse scenario in the most massive and densest clump C1. The estimated infall velocity and mass infall rate are 0.31 km s −1 and 7.2×10 −4 M e yr −1 , respectively. In clump C1, a hot molecular core (SMA1) is revealed by the Submillimeter Array observations and an outflow-driving high-mass protostar is located at the center of SMA1. The mass of the protostar is estimated to be 11-15 M e and it is still growing with an accretion rate of 7×10 −5 M e yr −1 . The coexistent infall in filaments, clump C1, and the central hot core in G22 suggests that pre-assembled mass reservoirs (i.e., high-mass starless cores) may not be required to form high-mass stars. In the course of high-mass star formation, the central protostar, the core, and the clump can simultaneously grow in mass via core-fed/disk accretion, clump-fed accretion, and filamentary/cloud collapse.

We report a sample of 463 high-mass starless clump (HMSC) candidates within l 60 60 - < <  and b 1 1 - < < . This sample has been singled out from 10,861 ATLASGAL clumps. None of these sources are associated with any known star-forming activities collected in SIMBAD and young stellar objects identified using color-based criteria. We also make sure that the HMSC candidates have neither point sources at 24 and 70 μmnor strong extended emission at 24 μm. Most of the identified HMSCs are infrared dark, and some are even dark at 70 μm. Their distribution shows crowding in Galactic spiral arms and toward the Galactic center and some wellknown star-forming complexes. Many HMSCs are associated with large-scale filaments. Some basic parameters were attained from column density and dust temperature maps constructed via fitting far-infrared and submillimeter continuum data to modified blackbodies. The HMSC candidates have sizes, masses, and densities similar to clumps associated with Class II methanol masers and HIIregions, suggesting that they will evolve into star-forming clumps. More than 90% of the HMSC candidates have densities above some proposed thresholds for forming highmass stars. With dust temperatures and luminosity-to-mass ratios significantly lower than that for star-forming sources, the HMSC candidates are externally heated and genuinely at very early stages of high-mass star formation. Twenty sources with equivalent radii r 0.15 eq < pc and mass surface densities 0.08 S > g cm −2 could be possible high-mass starless cores. Further investigations toward these HMSCs would undoubtedly shed light on comprehensively understanding the birth of high-mass stars.

Context. Triggered star formation around H ii regions could be an important process. The Galactic H ii region RCW 79 is a prototypical object for triggered high-mass star formation. Aims. We aim to obtain a census of the young stellar population observed at the edges of the H ii region and to determine the properties of the young sources in order to characterize the star formation processes that take place at the edges of this ionized region. Methods. We take advantage of Herschel data from the surveys HOBYS, "Evolution of Interstellar Dust", and Hi-Gal to extract compact sources. We use the algorithm getsources. We complement the Herschel data with archival 2MASS, Spitzer, and WISE data to determine the physical parameters of the sources (e.g., envelope mass, dust temperature, and luminosity) by fitting the spectral energy distribution. Results. We created the dust temperature and column density maps along with the column density probability distribution function (PDF) for the entire RCW 79 region. We obtained a sample of 50 compact sources in this region, 96% of which are situated in the ionization-compressed layer of cold and dense gas that is characterized by the column density PDF with a double-peaked lognormal distribution. The 50 sources have sizes of ∼ 0.1 − 0.4 pc with a typical value of ∼ 0.2 pc, temperatures of ∼ 11 − 26 K, envelope masses of ∼ 6 − 760 M , densities of ∼ 0.1 − 44 × 10 5 cm −3 , and luminosities of ∼ 19 − 12712 L . The sources are classified into 16 class 0, 19 intermediate, and 15 class I objects. Their distribution follows the evolutionary tracks in the diagram of bolometric luminosity versus envelope mass (L bol − Menv) well. A mass threshold of 140 M , determined from the L bol − Menv diagram, yields 12 candidate massive dense cores that may form high-mass stars. The core formation efficiency (CFE) for the 8 massive condensations shows an increasing trend of the CFE with density. This suggests that the denser the condensation, the higher the fraction of its mass transformation into dense cores, as previously observed in other high-mass star-forming regions.

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We investigate the presence of hub-filament systems in a large sample of 146 active proto-clusters, using H13CO+ J=1-0 molecular line data obtained from the ATOMS survey. We find that filaments are ubiquitous in proto-clusters, and hub-filament systems are very common from dense core scales (∼0.1 pc) to clump/cloud scales (∼1–10 pc). The proportion of proto-clusters containing hub-filament systems decreases with increasing dust temperature (Td) and luminosity-to-mass ratios (L/M) of clumps, indicating that stellar feedback from H ii regions gradually destroys the hub-filament systems as proto-clusters evolve. Clear velocity gradients are seen along the longest filaments with a mean velocity gradient of 8.71 km s−1 pc−1 and a median velocity gradient of 5.54 km s−1 pc−1. We find that velocity gradients are small for filament lengths larger than ∼1 pc, probably hinting at the existence of inertial inflows, although we cannot determine whether the latter are driven by large-scale turbulence or large-scale gravitational contraction. In contrast, velocity gradients below ∼1 pc dramatically increase as filament lengths decrease, indicating that the gravity of the hubs or cores starts to dominate gas infall at small scales. We suggest that self-similar hub-filament systems and filamentary accretion at all scales may play a key role in high-mass star formation.

To understand the nature of SiO emission, we conducted ACA observations of the SiO (2-1) lines toward 146 massive star-forming regions, as part of the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey. We detected SiO emission in 128 (87.7${{\ \rm per\ cent}}$) sources and identified 171 SiO clumps, 105 of which are spatially separated from 3 mm continuum emission. A large amount of the SiO line profiles (60${{\ \rm per\ cent}}$) are non-Gaussian. The velocity dispersion of the SiO lines ranges from 0.3 to 5.43 km s−1. In 63 sources the SiO clumps are associated with H ii regions characterized by H40α emission. We find that 68${{\ \rm per\ cent}}$ (116) of the SiO clumps are associated with strong outflows. The median velocity dispersion of the SiO line for outflow sources and non-outflow sources is 1.91 km s−1 and 0.99 km s−1, respectively. These results indicate that outflow activities could be connected to strongly shocked gas. The velocity dispersion and [SiO]/[H13CO+] intensity ratio do not show any correlation with the dust temperature and particle number density of clumps. We find a positive correlation between the SiO line luminosity and the bolometric luminosity, implying stronger shock activities are associated with more luminous proto-clusters. The SiO clumps in associations with H ii regions were found to show a steeper feature in $L_\mbox{sio}$/$L_\mbox{bol}$. The SiO line luminosity and the fraction of shocked gas have no apparent evidence of correlation with the evolutionary stages traced by luminosity to mass ratio ($L_\mbox{bol}/M$).

We present the spectroscopic observations for 11 confirmed globular clusters of M31 with the OMR spectrograph on 2.16m telescope at Xinglong site of National Astronomical Observatories, Chinese Academy of Sciences. Nine of our sample clusters are located in the halo of M31 and the most remote one is out to a projected radius of 78.75 kpc from the galactic center. For all our sample clusters, we measured the Lick absorption-line indices and the radial velocities. It is noted that most GCs of our sample are distinct from the HI rotation curve of M31 galaxy, especially for B514, MCGC5, H12 and B517, suggesting that most of our sample clusters do not have kinematic association with the star forming young disk of the galaxy. We fitted the absorption line indices with the updated stellar population model Thomas et al. (2010) with two different tracks of Cassisi and Padova, separately, by applying the χ 2 −minimization method. The fitting results show that all our sample clusters are older than 10 Gyr, and metal-poor (−0.91 ≤ [Fe/H] ≤ −2.38 dex). After merging the spectroscopic metallicity of our work with the previously published ones, we extended the cluster sample out to a projected radius of 117 kpc from the galaxy's center. We found the metallicity gradient for all the confirmed clusters exists with a slope of −0.028 ± 0.001 dex kpc −1 . However, the slope turns to be −0.018 ± 0.001 dex kpc −1 for all the halo clusters, which is much shallower. If we only consider the outer halo clusters with r p > 25 kpc, the slope becomes −0.010 ± 0.002 dex kpc −1 and if one cluster G001 is excluded from the outer halo sample, the slope is −0.004 ± 0.002 dex kpc −1 . Thus we conclude that metallicity gradient for M31 outer halo clusters is not significant, which agrees well with the previous findings.

Filaments play an important role in star formation, but the formation process of filaments themselves is still unclear. The high-mass star forming clump G286.21+0.17 (G286 for short) that contains an “L” type filament was thought to undergo global collapse. Our high resolution ALMA band 3 observations resolve the gas kinematics of G286 and reveal two sub-clumps with very different velocities inside it. We find that the “blue profile” (an indicator of gas infall) of HCO+ lines in single dish observations of G286 is actually caused by gas emission from the two sub-clumps rather than gas infall. We advise great caution in interpreting gas kinematics (e.g. infall) from line profiles toward distant massive clumps in single dish observations. Energetic outflows are identified in G286 but the outflows are not strong enough to drive expansion of the two sub-clumps. The two parts of the “L” type filament (“NW-SE” and “NE-SW” filaments) show prominent velocity gradients perpendicular to their major axes, indicating that they are likely formed due to large-scale compression flows. We argue that the large-scale compression flows could be induced by the expansion of nearby giant H ii regions. The “NW-SE” and “NE-SW” filaments seem to be in collision, and a large amount of gas has been accumulated in the junction region where the most massive core G286c1 forms.