The relative importance of primordial molecular cloud fragmentation versus large-scale accretion still remains to be assessed in the context of massive core/star formation. Studying the kinematics of the dense gas surrounding massive-star progenitors can tell us the extent to which large-scale flow of material impacts the growth in mass of star-forming cores. Here we present a comprehensive dataset of the 5500(±800) M infrared dark cloud SDC335.579-0.272 (hereafter SDC335), which exhibits a network of cold, dense, parsec-long filaments. Atacama Large Millimeter Array (ALMA) Cycle 0 observations reveal two massive star-forming cores, MM1 and MM2, sitting at the centre of SDC335 where the filaments intersect. With a gas mass of 545( +770 −385 ) M contained within a source diameter of 0.05 pc, MM1 is one of the most massive, compact protostellar cores ever observed in the Galaxy. As a whole, SDC335 could potentially form an OB cluster similar to the Trapezium cluster in Orion. ALMA and Mopra single-dish observations of the SDC335 dense gas furthermore reveal that the kinematics of this hub-filament system are consistent with a global collapse of the cloud. These molecular-line data point towards an infall velocity V inf = 0.7(±0.2) km s −1 , and a total mass infall rateṀ inf 2.5(±1.0) × 10 −3 M yr −1 towards the central pc-size region of SDC335. This infall rate brings 750(±300) M of gas to the centre of the cloud per free-fall time (t ff = 3 × 10 5 yr). This is enough to double the mass already present in the central pc-size region in 3.5 +2.2 −1.0 × t ff . These values suggest that the global collapse of SDC335 over the past million year resulted in the formation of an early O-type star progenitor at the centre of the cloud's gravitational potential well.

A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ∼15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ∼350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

We present the second portion of an unbiased survey of the Galactic plane for 6668‐MHz methanol masers. This section of the survey spans the longitude range 6° to 20°. We report the detection of 119 maser sources, of which 42 are new discoveries. The masers are tightly constrained to the Galactic plane, with only four outside a latitude range of ±1°. This longitude region includes the brightest known 6668‐MHz methanol maser, 9.621+0.196, as well as the two brightest newly discovered sources in the southern survey as a whole. We list all the sources associated with the 3‐kpc arms within ±15° longitude and consider further candidates beyond 15° longitude. We identify three new sources associated with the Galactic bar and comment on the density of masers in relation to the bar orientation.

We present the fifth portion of an unbiased survey of the Galactic plane, |b| ≤ 2• , for 6668-MHz methanol masers. This section of the survey completes the Galactic longitude range visible to the Parkes radio telescope, incorporating the longitude range 20• -60• . Within this section of the survey we find 265 methanol masers, 64 new to the survey, bringing the total number of methanol masers detected across the full longitude coverage (186• , through 0 • , to 60 • ) to 972 sources.

We have conducted a Galactic plane survey of methanol masers at 6668 MHz using a seven‐beam receiver on the Parkes telescope. Here we present results from the first part, which provides sensitive unbiased coverage of a large region around the Galactic Centre. Details are given for 183 methanol maser sites in the longitude range 345° through the Galactic Centre to 6°. Within 6° of the Galactic Centre, we found 88 maser sites, of which more than half (48) are new discoveries. The masers are confined to a narrow Galactic latitude range, indicative of many sources at the Galactic Centre distance and beyond, and confined to a thin disc population; there is no high‐latitude population that might be ascribed to the Galactic bulge. Within 2° of the Galactic Centre the maser velocities all lie between −60 and +77 km s−1, a range much smaller than the 540 km s−1 range observed in CO. Elsewhere, the maser with highest positive velocity (+107 km s−1) occurs, surprisingly, near longitude 355° and is probably attributable to the Galactic bar. The maser with the most negative velocity (−127 km s−1) is near longitude 346°, within the longitude–velocity locus of the near side of the ‘3‐kpc arm’. It has the most extreme velocity of a clear population of masers associated with the near and far sides of the 3‐kpc arm. Closer to the Galactic Centre the maser space density is generally low, except within 0.25 kpc of the Galactic Centre itself, the ‘Galactic Centre zone’, where it is 50 times higher, which is hinted at by the longitude distribution, and confirmed by the unusual velocities.