We study the core mass function (CMF) of the massive protocluster G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array via 1.3 mm continuum emission at a resolution of 1.0 (2500 au). We have mapped a field of 5.3 ×5.3 centered on the protocluster clump. We measure the CMF in the central region, exploring various core detection algorithms, which give source numbers ranging from 60 to 125, depending on parameter selection. We estimate completeness corrections due to imperfect flux recovery and core identification via artificial core insertion experiments. For masses M 1 M , the fiducial dendrogram-identified CMF can be fit with a power law of the form dN/dlogM ∝ M −α with α 1.24±0.17, slightly shallower than, but still consistent with, the index of the Salpeter stellar initial mass function of 1.35. Clumpfind-identified CMFs are significantly shallower with α 0.64 ± 0.13. While raw CMFs show a peak near 1 M , completeness-corrected CMFs are consistent with a single power law extending down to ∼ 0.5 M , with only a tentative indication of a shallowing of the slope around ∼ 1 M . We discuss the implications of these results for star and star cluster formation theories.

We study the probability distribution function (PDF) of mass surface densities, Σ, of infrared dark cloud (IRDC) G028.37+00.07 and its surrounding giant molecular cloud. This PDF constrains the physical processes, such as turbulence, magnetic fields and self-gravity, that are expected to be controlling cloud structure and star formation activity. The chosen IRDC is of particular interest since it has almost 100,000 solar masses within a radius of 8 parsecs, making it one of the most massive, dense molecular structures known and is thus a potential site for the formation of a "super star cluster." We study Σ in two ways. First, we use a combination of NIR and MIR extinction maps that are able to probe the bulk of the cloud structure up to Σ ∼ 1 g cm −2 (A V ≃ 200 mag). Second, we study the FIR and sub-mm dust continuum emission from the cloud utilizing Herschel PACS and SPIRE images and paying careful attention to the effects of foreground and background contamination. We find that the PDFs from both methods, applied over a ∼ 20 ′ (30 pc)-sized region that contains ≃ 1.5 × 10 5 M ⊙ and encloses a minimum closed contour with Σ ≃ 0.013 g cm −2 (A V ≃ 3 mag), shows a log-normal shape with the peak measured at Σ ≃ 0.021 g cm −2 (A V ≃ 4.7 mag). There is tentative evidence for the presence of a high-Σ power law tail that contains from ∼ 3% to 8% of the mass of the cloud material. We discuss the implications of these results for the physical processes occurring in this cloud.

Aims. Infrared dark clouds represent the earliest stages of high-mass star formation. Detailed observations of their physical conditions on all physical scales are required to improve our understanding of their role in fueling star formation. Methods. We investigate the large-scale structure of the IRDC G035.39-00.33, probing the dense gas with the classical ammonia thermometer. This allows us to put reliable constraints on the temperature of the extended, pc-scale dense gas reservoir and to probe the magnitude of its non-thermal motions. Available far-infrared observations can be used in tandem with the observed ammonia emission to estimate the total gas mass contained in G035.39-00.33. Results. We identify a main velocity component as a prominent filament, manifested as an ammonia emission intensity ridge spanning more than 6 pc, consistent with the previous studies on the Northern part of the cloud. A number of additional line-of-sight components are found, and a large scale, linear velocity gradient of ∼0.2 km s −1 pc −1 is found along the ridge of the IRDC. In contrast to the dust temperature map, an ammonia-derived kinetic temperature map, presented for the entirety of the cloud, reveals local temperature enhancements towards the massive protostellar cores. We show that without properly accounting for the line of sight contamination, the dust temperature is 2-3 K larger than the gas temperature measured with NH 3 . Conclusions. While both the large scale kinematics and temperature structure are consistent with that of starless dark filaments, the kinetic gas temperature profile on smaller scales is suggestive of tracing the heating mechanism coincident with the locations of massive protostellar cores.

We discuss the first results from our mid-infrared imaging survey of Milky Way Giant H II regions with our detailed analysis of W51A, which is one of the largest GH II regions in our Galaxy. We used the FORCAST instrument on SOFIA to obtain 20 and 37 µm images of the central 10 × 20 area, which encompasses both of the G49.5-0.4 and G49.4-0.3 sub-regions. Based on these new data, and in conjunction with previous multi-wavelength observations, we conjecture on the physical nature of several individual sources and sub-components within W 51 A. We find that extinction seems to play an important role in the observed structures we see in the near-to mid-infrared, both globally and locally. We used the SOFIA photometry combined with Spitzer -IRAC and Herschel -PACS photometry data to construct spectral energy distributions (SEDs) of sub-components and point sources detected in the SOFIA images. We fit those SEDs with young stellar object models, and found 41 sources that are likely to be massive young stellar objects, many of which are identified as such in this work for the first time. Close to half of the massive young stellar objects do not have detectable radio continuum emission at cm wavelengths, implying a very young state of formation. We derived luminosity-to-mass ratio and virial parameters of the extended radio sub-regions of W51A to estimate their relative ages.

We present SOFIA-upGREAT observations of [CII] emission of Infrared Dark Cloud (IRDC) G035.39-00.33, designed to trace its atomic gas envelope and thus test models of the origins of such clouds. Several velocity components of [CII] emission are detected, tracing structures that are at a wide range of distances in the Galactic plane. We find a main component that is likely associated with the IRDC and its immediate surroundings. This strongest emission component has a velocity similar to that of the 13 CO(2-1) emission of the IRDC, but offset by ∼ 3 km s −1 and with a larger velocity width of ∼ 9 km s −1 . The spatial distribution of the [CII] emission of this component is also offset predominantly to one side of the dense filamentary structure of the IRDC. The CII column density is estimated to be of the order of ∼ 10 17 − 10 18 cm −2 . We compare these results to the [CII] emission from numerical simulations of magnetized, dense gas filaments formed from giant molecular cloud (GMC) collisions, finding similar spatial and kinematic offsets. These observations and modeling of [CII] add further to the evidence that IRDC G035.39-00.33 has been formed by a process of GMC-GMC collision, which may thus be an important mechanism for initiating star cluster formation.