The ALMA Survey of 70 µm dark High-mass clumps in Early Stages (ASHES) has been designed to systematically characterize the earliest stages and to constrain theories of high-mass star formation. A deep understanding of highmass star formation requires the study of the clustered mode, which is the most commonly found in nature. A total of 12 massive (>500 M ), cold (≤15 K), 3.6-70 µm dark prestellar clump candidates, embedded in infrared dark clouds (IRDCs), were carefully selected in the pilot survey to be observed with the Atacama Large Millimeter/sub-millimeter Array (ALMA). Exploiting the unique capabilities of ALMA, we have mosaiced each clump (∼1 arcmin 2 ) in dust continuum and line emission with the 12 m, 7 m, and Total Power arrays at 224 GHz (1.34 mm), resulting in ∼1. 2 angular resolution (∼4800 AU at the average source distance of 4 kpc). As the first paper of the series, we concentrate on the dust continuum emission to reveal the clump fragmentation. We have detected a total of 294 cores, from which 84 (29%) are categorized as protostellar based on outflow activity or "warm core" line emission. The remaining 210 (71%) are considered prestellar core candidates. The number of detected cores is independent of the mass sensitivity range of the observations and, on average, more massive clumps tend to form more cores. We find no correlation between the mass of the host clump and the most massive embedded core. We find a large population of low-mass (<1 M ) cores and no high-mass (>30 M ) prestellar cores. The most massive prestellar core has a mass of 11 M . From the prestellar core mass function, we derive a power law index of 1.17 ± 0.10, slightly shallower than the Salpeter index of 1.35. We have used the minimum spanning tree technique to characterize the separation between cores and their spatial distribution, and to derive mass segregation ratios. While there is a range of core masses and core separations detected in the sample, the mean separation and mean mass of cores per clump are well explained

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Context. The giant molecular cloud Sagittarius B2 (hereafter Sgr B2) is the most massive region with ongoing high-mass star formation in the Galaxy. In the southern region of the 40-pc large envelope of Sgr B2, we encounter the Sgr B2(DS) region, which hosts more than 60 high-mass protostellar cores distributed in an arc shape around an extended H II region. Hints of non-thermal emission have been found in the H II region associated with Sgr B2(DS). Aims. We seek to characterize the spatial structure and the spectral energy distribution of the radio continuum emission in Sgr B2(DS). We aim to disentangle the contribution from the thermal and non-thermal radiation, as well as to study the origin of the non-thermal radiation. Methods. We used the Very Large Array in its CnB and D configurations, and in the frequency bands C (4–8 GHz) and X (8–12 GHz) to observe the whole Sgr B2 complex. Continuum and radio recombination line maps are obtained. Results. We detect radio continuum emission in Sgr B2(DS) in a bubble-shaped structure. From 4 to 12 GHz, we derive a spectral index between − 1.2 and − 0.4, indicating the presence of non-thermal emission. We decomposed the contribution from thermal and non-thermal emission, and find that the thermal component is clumpy and more concentrated, while the non-thermal component is more extended and diffuse. The radio recombination lines in the region are found to be not in local thermodynamic equilibrium but stimulated by the non-thermal emission. Conclusions. Sgr B2(DS) shows a mixture of thermal and non-thermal emission at radio wavelengths. The thermal free–free emission is likely tracing an H II region ionized by an O 7 star, while the non-thermal emission can be generated by relativistic electrons created through first-order Fermi acceleration. We have developed a simple model of the Sgr B2(DS) region and found that first-order Fermi acceleration can reproduce the observed flux density and spectral index.

The SEDIGISM (Structure, Excitation and Dynamics of the Inner Galactic Interstellar Medium) survey used the APEX telescope to map 84 deg2 of the Galactic plane between ℓ = −60○ and ℓ = +31○ in several molecular transitions, including 13CO (2 – 1) and C18O (2 – 1), thus probing the moderately dense (∼103 cm−3) component of the interstellar medium. With an angular resolution of 30″ and a typical 1σ sensitivity of 0.8–1.0 K at 0.25 km s−1 velocity resolution, it gives access to a wide range of structures, from individual star-forming clumps to giant molecular clouds and complexes. The coverage includes a good fraction of the first and fourth Galactic quadrants, allowing us to constrain the large scale distribution of cold molecular gas in the inner Galaxy. In this paper we provide an updated overview of the full survey and the data reduction procedures used. We also assess the quality of these data and describe the data products that are being made publicly available as part of this first data release (DR1). We present integrated maps and position-velocity maps of the molecular gas and use these to investigate the correlation between the molecular gas and the large scale structural features of the Milky Way such as the spiral arms, Galactic bar and Galactic centre. We find that approximately 60 per cent of the molecular gas is associated with the spiral arms and these appear as strong intensity peaks in the derived Galactocentric distribution. We also find strong peaks in intensity at specific longitudes that correspond to the Galactic centre and well known star forming complexes, revealing that the 13CO emission is concentrated in a small number of complexes rather than evenly distributed along spiral arms.