SPLASH (the Southern Parkes Large-Area Survey in Hydroxyl) is a sensitive, unbiased and fully-sampled survey of the Southern Galactic Plane and Galactic Centre in all four ground-state transitions of the hydroxyl (OH) radical. The survey provides a deep census of 1612-, 1665-, 1667-and 1720-MHz OH absorption and emission from the Galactic ISM, and is also an unbiased search for maser sources in these transitions. We present here first results from the SPLASH pilot region, which covers Galactic longitudes 334 • to 344 • and latitudes ±2 • . Diffuse OH is widely detected in all four transitions, with optical depths that are always small (averaged over the Parkes beam), and with departures from LTE common even in the 1665-and 1667-MHz main lines. To a 3σ sensitivity of ∼ 30 mK, we find no evidence of OH envelopes extending beyond the CO-bright regions of molecular cloud complexes, and conclude that the similarity of the OH excitation temperature and the level of the continuum background is at least partly responsible for this. We detect masers and maser candidates in all four transitions, approximately 50 per cent of which are new detections. This implies that SPLASH will produce a substantial increase in the known population of ground-state OH masers in the Southern Galactic Plane.

We present MeerKAT 1.28 GHz total-intensity, polarization, and spectral-index images covering the giant (projected length l ≈ 1.57 Mpc) X-shaped radio source PKS 2014−55 with an unprecedented combination of brightness sensitivity and angular resolution. They show the clear ‘double boomerang’ morphology of hydrodynamical backflows from the straight main jets deflected by the large and oblique hot-gas halo of the host galaxy PGC 064440. The magnetic field orientation in PKS 2014−55 follows the flow lines from the jets through the secondary wings. The radio source is embedded in faint ($T_\mathrm{b} \approx 0.5 \mathrm{\, K}$) cocoons having the uniform brightness temperature and sharp outer edges characteristic of subsonic expansion into the ambient intragroup medium. The position angle of the much smaller (l ∼ 25 kpc) restarted central source is within 5° of the main jets, ruling out models that invoke jet re-orientation or two independent jets. Compression and turbulence in the backflows probably produce the irregular and low polarization bright region behind the apex of each boomerang as well as several features in the flow with bright heads and dark tails.

MeerKAT’s large number (64) of 13.5 m diameter antennas, spanning 8 km with a densely packed 1 km core, create a powerful instrument for wide-area surveys, with high sensitivity over a wide range of angular scales. The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is a programme of long-track MeerKAT L-band (900−1670 MHz) observations of 115 galaxy clusters, observed for ∼6−10 h each in full polarisation. The first legacy product data release (DR1), made available with this paper, includes the MeerKAT visibilities, basic image cubes at ∼8″ resolution, and enhanced spectral and polarisation image cubes at ∼8″ and 15″ resolutions. Typical sensitivities for the full-resolution MGCLS image products range from ∼3−5 μJy beam−1. The basic cubes are full-field and span 2° × 2°. The enhanced products consist of the inner 1.2° × 1.2° field of view, corrected for the primary beam. The survey is fully sensitive to structures up to ∼10′ scales, and the wide bandwidth allows spectral and Faraday rotation mapping. Relatively narrow frequency channels (209 kHz) are also used to provide H I mapping in windows of 0 < z < 0.09 and 0.19 < z < 0.48. In this paper, we provide an overview of the survey and the DR1 products, including caveats for usage. We present some initial results from the survey, both for their intrinsic scientific value and to highlight the capabilities for further exploration with these data. These include a primary-beam-corrected compact source catalogue of ∼626 000 sources for the full survey and an optical and infrared cross-matched catalogue for compact sources in the primary-beam-corrected areas of Abell 209 and Abell S295. We examine dust unbiased star-formation rates as a function of cluster-centric radius in Abell 209, extending out to 3.5 R 200. We find no dependence of the star-formation rate on distance from the cluster centre, and we observe a small excess of the radio-to-100 μm flux ratio towards the centre of Abell 209 that may reflect a ram pressure enhancement in the denser environment. We detect diffuse cluster radio emission in 62 of the surveyed systems and present a catalogue of the 99 diffuse cluster emission structures, of which 56 are new. These include mini-halos, halos, relics, and other diffuse structures for which no suitable characterisation currently exists. We highlight some of the radio galaxies that challenge current paradigms, such as trident-shaped structures, jets that remain well collimated far beyond their bending radius, and filamentary features linked to radio galaxies that likely illuminate magnetic flux tubes in the intracluster medium. We also present early results from the H I analysis of four clusters, which show a wide variety of H I mass distributions that reflect both sensitivity and intrinsic cluster effects, and the serendipitous discovery of a group in the foreground of Abell 3365.

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The high-mass star-forming site G009.62+00.20 E hosts the 6.7 GHz methanol maser source with the greatest flux density in the Galaxy which has been flaring periodically over the last ten years. We performed high-resolution astrometric measurements of the CH 3 OH, H 2 O, and OH maser emission and 7 mm continuum in the region. The radio continuum emission was resolved in two sources separated by 1300 AU. The CH 3 OH maser cloudlets are distributed along two north-south ridges of emission to the east and west of the strongest radio continuum component. This component likely pinpoints a massive young stellar object which heats up its dusty envelope, providing a constant IR pumping for the Class II CH 3 OH maser transitions. We suggest that the periodic maser activity may be accounted for by an independent, pulsating, IR radiation field provided by a bloated protostar in the vicinity of the brightest masers. We also report about the discovery of an elliptical distribution of CH 3 OH maser emission in the region of periodic variability.

The inner ∼200 pc region of the Galaxy contains a 4 million M⊙ supermassive black hole (SMBH), significant quantities of molecular gas, and star formation and cosmic-ray energy densities that are roughly two orders of magnitude higher than the corresponding levels in the Galactic disk. At a distance of only 8.2 kpc, the region presents astronomers with a unique opportunity to study a diverse range of energetic astrophysical phenomena, from stellar objects in extreme environments, to the SMBH and star-formation-driven feedback processes that are known to influence the evolution of galaxies as a whole. We present a new survey of the Galactic center conducted with the South African MeerKAT radio telescope. Radio imaging offers a view that is unaffected by the large quantities of dust that obscure the region at other wavelengths, and a scene of striking complexity is revealed. We produce total-intensity and spectral-index mosaics of the region from 20 pointings (144 hr on-target in total), covering 6.5 square degrees with an angular resolution of 4″ at a central frequency of 1.28 GHz. Many new features are revealed for the first time due to a combination of MeerKAT’s high sensitivity, exceptional u, v-plane coverage, and geographical vantage point. We highlight some initial survey results, including new supernova remnant candidates, many new nonthermal filament complexes, and enhanced views of the Radio Arc bubble, Sagittarius A, and Sagittarius B regions. This project is a South African Radio Astronomy Observatory public legacy survey, and the image products are made available with this article.

Context. Weak and compact radio continuum and H2O masers are preferred tracers of the outflow activity nearby very young stars. Aims. We want to image the centimeter free–free continuum emission in the range 1–7 cm (26–4 GHz), which arises in the inner few 1000 au from those young stars also associated with bright H2O masers. We seek to study the radio continuum properties in combination with the H2O maser kinematics to quantify the outflow energetics powered by single young stars. Methods. We made use of the Karl G. Jansky Very Large Array (VLA) in the B configuration at K band and the A configuration at both Ku and C bands in order to image the radio continuum emission toward 25 H2O maser sites with an angular resolution and thermal rms on the order of 0.′′1 and 10 μJy beam−1, respectively. These targets add to our pilot study of 11 maser sites previously presented. The sample of H2O maser sites was selected among those regions that have accurate distance measurements, obtained through maser trigonometric parallaxes, and H2O maser luminosities in excess of 10−6 L⊙. Results. We present high-resolution radio continuum images of 33 sources belonging to 25 star-forming regions. In each region, we detect radio continuum emission within a few 1000 au of the H2O masers’ position; 50% of the radio continuum sources are associated with bolometric luminosities exceeding 5 × 103 L⊙, including W33A and G240.32 + 0.07. We provide a detailed spectral index analysis for each radio continuum source, based on the integrated fluxes at each frequency, and produce spectral index maps with the multifrequency synthesis deconvolution algorithm of CASA. The radio continuum emission traces thermal bremsstrahlung in (proto)stellar winds and jets that have flux densities at 22 GHz below 3 mJy and spectral index values between − 0.1 and 1.3. We prove a strong correlation (r > 0.8) between the radio continuum luminosity (Lrad) and the H2O maser luminosity (LH2O) of (L8 GHz∕mJy kpc2) = 103.8 × (LH2O L⊙)0.74. This power-law relation is similar to that between the radio continuum and bolometric luminosities, which confirms earlier studies. Since H2O masers are excited through shocks driven by (proto)stellar winds and jets, these results provide support to the idea that the radio continuum emission around young stars is dominated by shock ionization, and this holds over several orders of magnitude of stellar luminosites (1–105 L⊙).

We have used the Australia Telescope Compact Array to undertake the first highresolution observations of the 19.9-GHz (2 1 − 3 0 E) methanol maser transition. The emission is coincident with the location of the targeted 6.7-GHz methanol masers to within 0.2 arcseconds in absolute position. We find that the relative distribution of the 19.9-GHz maser emission in our sample differs from that observed in the 6.7-GHz transition, in contrast to the similar distribution often seen in the 6.7-and 12.2-GHz methanol masers in many sources. We also find that the peak velocity for the 19.9-GHz methanol masers is frequently different from that observed in other class II transitions in the same regions. These two results suggest that while 19.9-GHz methanol masers arise from the same general location as other class II transitions, they are likely not coincident on milliarcsecond scales; which has implications for multi-transitional modelling of class II methanol maser sources. We have investigated the properties of the OH and other class II methanol transitions for those 107-GHz methanol masers with and without an associated 19.9-GHz methanol maser. On the basis of these comparisons we suggest that the 19.9-GHz transition traces an evolutionary phase around the peak of the class II maser luminosity into its decline.