We report molecular line observations of the massive protostellar source G339.88-1.26 with the Atacama Large Millimeter/Submillimeter Array. The observations reveal a highly collimated SiO jet extending from the 1.3 mm continuum source, which connects to a slightly wider but still highly collimated CO outflow. Rotational features perpendicular to the outflow axis are detected in various molecular emissions, including SiO, SO 2 , H 2 S, CH 3 OH, and H 2 CO emissions. Based on their spatial distributions and kinematics, we find that they trace different parts of the envelope-disk system. The SiO emission traces the disk and inner envelope in addition to the jet. The CH 3 OH and H 2 CO emissions mostly trace the infalling-rotating envelope, and are enhanced around the transition region between envelope and disk, i.e., the centrifugal barrier. The SO 2 and H 2 S emissions are enhanced around the centrifugal barrier, and also trace the outer part of the disk. Envelope kinematics are consistent with rotating-infalling motion, while those of the disk are consistent with Keplerian rotation. The radius and velocity of the centrifugal barrier are estimated to be about 530 au and 6 km s −1 , leading to a central mass of about 11 M , consistent with estimates based on spectral energy distribution fitting. These results indicate that an ordered transition from an infalling-rotating envelope to a Keplerian disk through a centrifugal barrier, accompanied by changes of types of molecular line emissions, is a valid description of this massive protostellar source. This implies that at least some massive stars form in a similar way as low-mass stars via Core Accretion.

We study the core mass function (CMF) within 32 dense clumps in seven infrared dark clouds (IRDCs) with the Atacama Large Millimeter/submillimeter Array (ALMA) via 1.3 mm continuum emission at a resolution of ∼1 . We have identified 107 cores with the dendrogram algorithm, with a median radius of about 0.02 pc. Their masses range from 0.261 to 178 M . After applying completeness corrections, we fit the combined IRDC CMF with a power law of the form dN/d logM ∝ M −α and derive an index of α 0.86±0.11 for M ≥ 0.79M and α 0.70±0.13 for M ≥ 1.26M , which is a significantly more top-heavy distribution than the Salpeter stellar initial mass function (IMF) index of 1.35. We also make a direct comparison of these IRDC clump CMF results to those measured in the more evolved protocluster G286 derived with similar methods, which have α 1.29 ± 0.19 and 1.08 ± 0.27 in these mass ranges, respectively. These results provide a hint that, especially for the M ≥ 1.26 M range where completeness corrections are modest, the CMF in high pressure, early-stage environments of IRDC clumps may be top-heavy compared to that in the more evolved, global environment of the G286 protoclusters. However, larger samples of cores probing these different environments are needed to better establish the robustness of this potential CMF variation.

We present multi-wavelength images observed with SOFIA-FORCAST from ∼10 to 40 µm of seven high luminosity massive protostars, as part of the SOFIA Massive (SOMA) Star Formation Survey. Source morphologies at these wavelengths appear to be influenced by outflow cavities and extinction from dense gas surrounding the protostars. Using these images, we build spectral energy distributions (SEDs) of the protostars, also including archival data from Spitzer, Herschel and other facilities. Radiative transfer (RT) models of Zhang & Tan (2018), based on Turbulent Core Accretion theory, are then fit to the SEDs to estimate key properties of the protostars. Considering the best five models fit to each source, the protostars have masses m * ∼ 12 − 64 M accreting at rates ofṁ * ∼ 10 −4 − 10 −3 M yr −1 inside cores of initial masses M c ∼ 100 − 500 M embedded in clumps with mass arXiv:1901.01958v2 [astro-ph.GA] 18 Feb 2019 2 Liu et al.surface densities Σ cl ∼ 0.1 − 3 g cm −2 and span a luminosity range of 10 4 − 10 6 L . Compared with the first eight protostars in Paper I, the sources analyzed here are more luminous, and thus likely to be more massive protostars. They are often in a clustered environment or have a companion protostar relatively nearby. From the range of parameter space of the models, we do not see any evidence that Σ cl needs to be high to form these massive stars. For most sources the RT models provide reasonable fits to the SEDs, though the cold clump material often influences the long wavelength fitting. However, for sources in very clustered environments, the model SEDs may not be such a good description of the data, indicating potential limitations of the models for these regions.

We conduct a census of the high-mass protostellar population of the ∼ 70, 000 M Infrared Dark Cloud (IRDC) G028.37+00.07, identifying 35 sources based on their 70 µm emission, as reported in the Herschel Hi-Gal catalog of Molinari et al. (2016). We perform aperture photometry to construct spectral energy distributions (SEDs), which are then fit with the massive protostar models of Zhang & Tan (2018). We find that the sources span a range of isotropic luminosities from ∼ 20 to 4,500 L . The most luminous sources are predicted to have current protostellar masses of m * ∼ 10 M forming from cores of mass M c ∼ 40 to 400 M . The least luminous sources in our sample are predicted to be protostars with masses as low as ∼ 0.5 M forming from cores with M c ∼ 10 M , which are the minimum values explored in the protostellar model grid. The detected protostellar population has a total estimated protostellar mass of M * ∼ 100 M . Allowing for completeness corrections, which are constrained by comparison with an ALMA study in part of the cloud, we estimate a star formation efficiency per free-fall time of ∼ 3% in the IRDC. Finally, analyzing the spatial distribution of the sources, we find relatively low degrees of central concentration of the protostars. Thus, the most massive protostars do not appear to be especially centrally concentrated in the protocluster.

To study the early phases of massive star formation, we present ALMA observations of SiO(5−4) emission and VLA observations of 6 cm continuum emission toward 32 Infrared Dark Cloud clumps, spatially resolved down to ≲0.05 pc. Out of the 32 clumps, we detect SiO emission in 20 clumps, and in 11 of them the SiO emission is relatively strong and likely tracing protostellar outflows. Some SiO outflows are collimated, while others are less ordered. For the six strongest SiO outflows, we estimate basic outflow properties. In our entire sample, where there is SiO emission, we find 1.3 mm continuum and infrared emission nearby, but not vice versa. We build the spectral energy distributions (SEDs) of cores with 1.3 mm continuum emission and fit them with radiative transfer models. The low luminosities and stellar masses returned by SED fitting suggest these are early-stage protostars. We see a slight trend of increasing SiO line luminosity with bolometric luminosity, which suggests more powerful shocks in the vicinity of more massive YSOs. We do not see a clear relation between the SiO luminosity and the evolutionary stage indicated by L/M. We conclude that, as a protostar approaches a bolometric luminosity of ∼102 L ⊙, the shocks in the outflow are generally strong enough to form SiO emission. The VLA 6 cm observations toward the 15 clumps with the strongest SiO emission detect emission in four clumps, which is likely from shock-ionized jets associated with the more massive ones of these protostellar cores.