mJy Beam Research Articles

Unveiling the early-stage anatomy of a protocluster hub with ALMA

Abstract High-mass stars shape the interstellar medium in galaxies, and yet, largely because the initial conditions are poorly constrained, we do not know how they form. One possibility is that high-mass stars and star clusters form at the junction of filamentary networks, referred to as ‘hubs’. In this Letter we present the complex anatomy of a protocluster hub within an Infrared Dark Cloud (IRDC), G035.39−00.33, believed to be in an early phase of its evolution. We use high-angular resolution ({θmaj, θmin} = {1.4 arcsec, 0.8 arcsec} ∼ {0.02 pc, 0.01 pc}) and high-sensitivity (0.2 mJy beam−1; ∼0.2 Mȯ) 1.07 mm dust continuum observations from the Atacama Large Millimeter Array (ALMA) to identify a network of narrow, 0.028 ± 0.005 pc wide, filamentary structures. These are a factor of ≳3 narrower than the proposed ‘quasi-universal’ ∼0.1 pc width of interstellar filaments. Additionally, 28 compact objects are reported, spanning a mass range 0.3 Mȯ < Mc < 10.4 Mȯ. This indicates that at least some low-mass objects are forming coevally with more massive counterparts. Comparing to the popular ‘bead-on-a-string’ analogy, the protocluster hub is poorly represented by a monolithic clump embedded within a single filament. Instead, it comprises multiple intra-hub filaments, each of which retains its integrity as an independent structure and possesses its own embedded core population.

CONSTRAINTS ON PLANETESIMAL COLLISION MODELS IN DEBRIS DISKS

ABSTRACT Observations of debris disks offer a window into the physical and dynamical properties of planetesimals in extrasolar systems through the size distribution of dust grains. In particular, the millimeter spectral index of thermal dust emission encodes information on the grain size distribution. We have made new VLA observations of a sample of seven nearby debris disks at 9 mm, with resolution and ∼5 μJy beam−1rms. We combine these with archival ATCA observations of eight additional debris disks observed at 7 mm, together with up-to-date observations of all disks at (sub)millimeter wavelengths from the literature, to place tight constraints on the millimeter spectral indices and thus grain size distributions. The analysis gives a weighted mean for the slope of the power-law grain size distribution, , of , with a possible trend of decreasing q for later spectral type stars. We compare our results to a range of theoretical models of collisional cascades, from the standard self-similar, steady-state size distribution (q = 3.5) to solutions that incorporate more realistic physics such as alternative velocity distributions and material strengths, the possibility of a cutoff at small dust sizes from radiation pressure, and results from detailed dynamical calculations of specific disks. Such effects can lead to size distributions consistent with the data, and plausibly the observed scatter in spectral indices. For the AU Mic system, the VLA observations show clear evidence of a highly variable stellar emission component; this stellar activity obviates the need to invoke the presence of an asteroid belt to explain the previously reported compact millimeter source in this system.

ALMACAL I: FIRST DUAL-BAND NUMBER COUNTS FROM A DEEP AND WIDE ALMA SUBMILLIMETER SURVEY, FREE FROM COSMIC VARIANCE

ABSTRACT We have exploited ALMA calibration observations to carry out a novel, wide, and deep submillimeter (submm) survey, almacal. These calibration data comprise a large number of observations of calibrator fields in a variety of frequency bands and array configurations. By gathering together data acquired during multiple visits to many ALMA calibrators, it is possible to reach noise levels which allow the detection of faint, dusty, star-forming galaxies (DSFGs) over a significant area. In this paper, we outline our survey strategy and report the first results. We have analyzed data for 69 calibrators, reaching depths of ∼25 μJy beam−1 at sub-arcsec resolution. Adopting a conservative approach based on ≥5σ detections, we have found 8 and 11 DSFGs in ALMA bands 6 and 7, respectively, with flux densities S 1.2 mm ≥ 0.2 mJy. The faintest galaxies would have been missed by even the deepest Herschel surveys. Our cumulative number counts have been determined independently at 870 μm and 1.2 mm from a sparse sampling of the astronomical sky, and are thus relatively free of cosmic variance. The counts are lower than reported previously by a factor of at least 2×. Future analyses will yield large, secure samples of DSFGs with redshifts determined via the detection of submm spectral lines. Uniquely, our strategy then allows for morphological studies of very faint DSFGs—representative of more normal star-forming galaxies than conventional submm galaxies—in fields where self-calibration is feasible, yielding milliarcsecond spatial resolution.

European VLBI Network imaging of 6.7 GHz methanol masers

Methanol masers at 6.7 GHz are well known tracers of high-mass star-forming regions. However, their origin is still not clearly understood. We aimed to determine the morphology and velocity structure for a large sample of the maser emission with generally lower peak flux densities than those in previous surveys. Using the European VLBI Network we imaged the remaining sources (17) from a sample of sources that were selected from the unbiased survey using the Torun 32 m dish. Together they form a database of a total of 63 source images with high sensitivity, milliarcsecond angular resolution and very good spectral resolution for detailed studies. We studied in detail the properties of the maser clouds and calculated the mean and median values of the projected size (17.4 au and 5.5 au, respectively) as well as the FWHM of the line (0.373 km s$^{-1}$ and 0.315 km s$^{-1}$ for the mean and median values, respectively), testing whether it was consistent with Gaussian profile. We also found maser clouds with velocity gradients (71 per cent) that ranged from 0.005 km s$^{-1}$ au$^{-1}$ to 0.210 km s$^{-1}$ au$^{-1}$. We tested the kinematic models to explain the observed structures of the 6.7 GHz emission. There were targets where the morphology supported the scenario of a rotating and expanding disk or a bipolar outflow. Comparing the interferometric and single-dish spectra we found that, typically, 50-70 per cent of the flux was missing. This phenomena is not strongly related to the distance of the source. The EVN imaging reveals that in the complete sample of 63 sources the ring-like morphology appeared in 17 per cent of sources, arcs were seen in a further 8 per cent, and the structures were complex in 46 per cent cases. The UC HII regions coincide in position in the sky for 13 per cent of the sources. They are related both to extremely high and low luminosity masers from the sample.

A MILLISECOND INTERFEROMETRIC SEARCH FOR FAST RADIO BURSTS WITH THE VERY LARGE ARRAY

A MILLISECOND INTERFEROMETRIC SEARCH FOR FAST RADIO BURSTS WITH THE VERY LARGE ARRAY

Megahertz peaked-spectrum sources in the Boötes field I - a route towards finding high-redshift AGN

We present a 324.5 MHz image of the NOAO Bootes eld that was made using Very Large Array (VLA) P-band observations. The image has a resolution of 5:6 5:1 arcsec, a radius of 2:05 and a central noise of 0:2 mJy beam 1 . Both the resolution and noise of the image are an order of magnitude better than what was previously avail- able at this frequency and will serve as a valuable addition to the already extensive multiwavelength data that are available for this eld. The nal source catalogue con- tains 1370 sources and has a median 325 to 1400 MHz spectral index of -0.72. Using a radio colour-colour diagram of the unresolved sources in our catalogue, we identify 33 megahertz peaked-spectrum (MPS) sources. Based on the turnover frequency linear size relation for the gigahertz peaked-spectrum (GPS) and compact steep-spectrum (CSS) sources, we expect that the MPS sources that are compact on scales of tens of milliarcseconds should be young radio loud active galactic nuclei at high (z > 2) redshifts. Of the 33 MPS sources, we were able to determine redshifts for 24, with an average redshift of 1.3. Given that ve of the sources are at z > 2, that the four faint sources for which we could not nd redshifts are likely at even higher redshifts and that we could only select sources that are compact on a scale of 5 arcsec, there is encouraging evidence that the MPS method can be used to search for high-redshift sources.

Local Group dSph radio survey with ATCA – II. Non-thermal diffuse emission

Our closest neighbours, the Local Group dwarf spheroidal (dSph) galaxies, are extremely quiescent and dim objects, where thermal and non-thermal diffuse emissions lack, so far, of detection. In order to possibly study the dSph interstellar medium, deep observations are required. They could reveal non-thermal emissions associated with the very low level of star formation, or to particle dark matter annihilating or decaying in the dSph halo. In this work, we employ radio observations of six dSphs, conducted with the Australia Telescope Compact Array in the frequency band 1.1–3.1 GHz, to test the presence of a diffuse component over typical scales of few arcmin and at an rms sensitivity below 0.05 mJy beam−1. We observed the dSph fields with both a compact array and long baselines. Short spacings led to a synthesized beam of about 1 arcmin and were used for the extended emission search. The high-resolution data mapped background sources, which in turn were subtracted in the short-baseline maps, to reduce their confusion limit. We found no significant detection of a diffuse radio continuum component. After a detailed discussion on the modelling of the cosmic ray (CR) electron distribution and on the dSph magnetic properties, we present bounds on several physical quantities related to the dSphs, such that the total radio flux, the angular shape of the radio emissivity, the equipartition magnetic field, and the injection and equilibrium distributions of CR electrons. Finally, we discuss the connection to far-infrared and X-ray observations.

Early science with the Karoo Array Telescope: a mini-halo candidate in galaxy cluster Abell 3667

Abell 3667 is among the most well-studied galaxy clusters in the Southern Hemisphere. It is known to host two giant radio relics and a head-tail radio galaxy as the brightest cluster galaxy. Recent work has suggested the additional presence of a bridge of diffuse synchrotron emission connecting the North-Western radio relic with the cluster centre. In this work, we present full-polarization observations of Abell 3667 conducted with the Karoo Array Telescope at 1.33 and 1.82 GHz. Our results show both radio relics as well as the brightest cluster galaxy. We use ancillary higher-resolution data to subtract the emission from this galaxy, revealing a localised excess, which we tentatively identify as a radio mini-halo. This mini-halo candidate has an integrated flux density of $67.2\pm4.9$ mJy beam$^{-1}$ at 1.37 GHz, corresponding to a radio power of P$_{\rm{1.4\,GHz}}=4.28\pm0.31\times10^{23}$ W Hz$^{-1}$, consistent with established trends in mini-halo power scaling.

New insights from deep VLA data on the potentially recoiling black hole CID-42 in the COSMOS field

We present deep 3-GHz Karl G. Jansky Very Large Array (VLA) observations of the potentially recoiling black hole CID-42 in the Cosmic Evolution Survey (COSMOS) field. This galaxy shows two optical nuclei in the Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) image and a large velocity offset of ≈1300 km s−1 between the broad and narrow Hβ emission line although the spectrum is not spacially resolved (Civano et al. 2010). The new 3 GHz VLA data have a bandwidth of 2 GHz and to correctly interpret the flux densities imaging was done with two different methods: multiscale multifrequency (MSMF) synthesis and spectral windows (SPWs) stacking. The final resolutions and sensitivities of these maps are 0.7 arcsec with rms = 4.6 μJy beam−1 and 0.9 arcsec with rms = 4.8 μJy beam−1, respectively. With a 7σ detection, we find that the entire observed 3-GHz radio emission can be associated with the south-eastern component of CID-42, coincident with the detected X-ray emission. We use our 3 GHz data combined with other radio data from the literature ranging from 320 MHz to 9 GHz, which include the VLA, Very Long Baseline Array (VLBA) and Giant Metrewave Radio Telescope (GMRT) data, to construct a radio synchrotron spectrum of CID-42. The radio spectrum suggests a type I unobscured radio-quiet flat-spectrum active galactic nucleus (AGN) in the south-eastern component which may be surrounded by a more extended region of old synchrotron electron population or shocks generated by the outflow from the supermassive black hole (SMBH). Our data are consistent with the recoiling black hole picture but cannot rule out the presence of an obscured and radio-quiet SMBH in the north-western component.

LOFAR LOW-BAND ANTENNA OBSERVATIONS OF THE 3C 295 AND BOÖTES FIELDS: SOURCE COUNTS AND ULTRA-STEEP SPECTRUM SOURCES

We present LOFAR Low Band observations of the Bootes and 3C295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam$^{-1}$, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17 to 52 deg$^{2}$. From the observations we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and VLA 74 MHz differential source counts, scaling with a spectral index of $-0.7$. We find that a spectral index scaling of $-0.5$ is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens towards lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum ($\alpha < -1.1$) radio sources, that could be associated with massive high redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz and 1.4 GHz for sources in the Bo\"otes field. We cross-correlate these radio sources with optical and infrared catalogues and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the $ 0.7 \lesssim z \lesssim 2.5$ range.

THE HERSCHEL STRIPE 82 SURVEY (HerS): MAPS AND EARLY CATALOG

We present the first set of maps and band-merged catalog from the Herschel Stripe 82 Survey (HerS). Observations at 250, 350, and 500 micron were taken with the Spectral and Photometric Imaging Receiver (SPIRE) instrument aboard the Herschel Space Observatory. HerS covers 79 deg$^2$ along the SDSS Stripe 82 to a depth of 13.0, 12.9, and 14.8 mJy beam$^{-1}$ (including confusion) at 250, 350, and 500 micron, respectively. HerS was designed to measure correlations with external tracers of the dark matter density field --- either point-like (i.e., galaxies selected from radio to X-ray) or extended (i.e., clusters and gravitational lensing) --- in order to measure the bias and redshift distribution of intensities of infrared-emitting dusty star-forming galaxies and AGN. By locating HeRS in Stripe 82, we maximize the overlap with available and upcoming cosmological surveys. The band-merged catalog contains 3.3x10$^4$ sources detected at a significance of >3 $\sigma$ (including confusion noise). The maps and catalog are available at http://www.astro.caltech.edu/hers/

The Second Epoch Molonglo Galactic Plane Survey: Images and Candidate Supernova Remnants

AbstractThe second epoch Molonglo Galactic Plane Survey covers the area 245° ⩽l⩽ 365° and |b| ⩽ 10° at a frequency of 843 MHz and an angular resolution of 45 arcsec × 45 arcsec cosec(δ). The sensitivity varies between 1–2 mJy beam− 1depending on the presence of strong extended sources. This survey is currently the highest resolution and most sensitive large-scale continuum survey of the southern Galactic plane. In this paper, we present the images of the complete survey, including postage stamps of some new supernova remnant (SNR) candidates and a discussion of the highly structured features detected in the interstellar medium. The intersection of these two types of features is discussed in the context of the ‘missing’ SNR population in the Galaxy.

The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14 110 Compact Radio Sources over 6 100 Square Degrees

AbstractWe present the results of an approximately 6 100 deg2 104–196 MHz radio sky survey performed with the Murchison Widefield Array during instrument commissioning between 2012 September and 2012 December: the MWACS. The data were taken as meridian drift scans with two different 32-antenna sub-arrays that were available during the commissioning period. The survey covers approximately 20.5 h &lt; RA &lt; 8.5 h, − 58° &lt; Dec &lt; −14°over three frequency bands centred on 119, 150 and 180 MHz, with image resolutions of 6–3 arcmin. The catalogue has 3 arcmin angular resolution and a typical noise level of 40 mJy beam− 1, with reduced sensitivity near the field boundaries and bright sources. We describe the data reduction strategy, based upon mosaicked snapshots, flux density calibration, and source-finding method. We present a catalogue of flux density and spectral index measurements for 14 110 sources, extracted from the mosaic, 1 247 of which are sub-components of complexes of sources.

Beyond stacking: a maximum-likelihood method to constrain radio source counts below the detection threshold

We present a statistical method based on a maximum-likelihood approach to constrain the number counts of extragalactic sources below the nominal flux-density limit of continuum imaging surveys. We extract flux densities from a radio map using positional information from an auxiliary catalogue and show that we can model the number counts of this undetected population down to flux-density levels well below the detection threshold of the radio survey. We demonstrate the capabilities that our method will have with future generation wide-area radio surveys by performing simulations over various sky areas. We show that it is possible to accurately constrain the number counts of the simulated distribution down to one-tenth of the flux noise rms with just a sky area of 100 deg2. We then test the application of our method using data from the Faint Images of the Radio Sky at Twenty-Centimetres survey (FIRST). We extract flux densities from the FIRST map, sensitive to 150 μJy beam−1 (1 σ), using the positional information from a catalogue in the same field, also acquired at the same frequency, sensitive to 12 μJy beam−1 (1 σ). Implementing our method, with known source positions, we are able to recover the right differential number counts of the noise-dominated FIRST map fluxes down to a flux-density level which is one-tenth the FIRST detection threshold.

Do protostellar fountains shape the regional core mass function?

The emerging massive binary system associated with AFGL 961 signifies the latest generation of massive star and cluster formation in the Rosette Molecular Complex. We present the detection of a compact cluster of dusty cores toward the AFGL 961 region based on continuum imaging at 1.3 mm by the Submillimeter Array. The binary components of AFGL 961 are associated with the most intensive millimeter emission cores or envelopes, confirming that they are indeed in an early stage of evolution. The other massive cores, however, are found to congregate in the close vicinity of the central high-mass protostellar binary. They have no apparent infrared counterparts and are, in particular, well aligned transverse to the bipolar molecular outflows originating from AFGL 961. This provides evidence for a likely triggered origin of the massive cores. All 40 individual cores with masses ranging between 0.6 and 15 M⊙ were detected above a 3 σ level of 3.6 mJy beam−1 (or 0.4 M⊙), based on which we derive a total core mass of 107 M⊙ in the AFGL 961 region. As compared to the stellar initial mass function, a shallow slope of 1.8 is, however, derived from the best fit to the mass spectrum of the millimeter cores with a prestellar and/or protostellar origin. The flatter core mass distribution in the AFGL 961 region is attributed here to dynamic perturbations from the massive molecular outflows that originated from the massive protostellar binary, which may have altered the otherwise more quiescent conditions of core or star formation, enhanced the formation of more massive cores and, as a result, influenced the core mass distribution in its close vicinity.

E-MERLIN resolves Betelgeuse at λ 5 cm: hotspots at 5 R⋆

Abstract Convection, pulsation and magnetic fields have all been suggested as mechanisms for the transport of mass and energy from the optical photosphere of red supergiants, out to the region where the stellar wind is launched. We imaged the red supergiant Betelgeuse at 0.06–0.18 arcsec resolution, using e-Multi-Element Radio-Linked Interferometer Network (e-MERLIN) at 5.5–6.0 GHz, with a sensitivity of ∼10 μJy beam−1. Most of the radio emission comes from within an ellipse (0.235 × 0.218) arcsec2 (∼5 times the optical radius), with a flux density of 1.62 mJy, giving an average brightness temperature ∼1250 K. This radio photosphere contains two hotspots of 0.53 and 0.79 mJy beam−1, separated by 90 mas, with brightness temperatures 5400 ± 600 K and 3800 ± 500 K. Similar hotspots, at more than double the distance from the photosphere of those seen in any other regime, were detected by the less-sensitive ‘old’ MERLIN in 1992, 1995 and 1996 and many exceed the photospheric temperature of 3600 K. Such brightness temperatures are high enough to emanate from pockets of chromospheric plasma. Other possibilities include local shock heating, the convective dredge-up of hot material or exceptionally cool, low-density regions, transparent down to the hottest layer at ∼40 mas radius. We also detect an arc 0.2–0.3 arcsec to the SW, brightness temperature ∼150 K, in a similar direction to extensions seen on both smaller and larger scales in the infrared and in CO at mm wavelengths. These preliminary results will be followed by further e-MERLIN, Very Large Array and Atacama Large Millimeter/sub-millimeter Array (ALMA) observations to help resolve the problem of mass elevation from 1 to 10 R⋆ in red supergiants.

A deep ATCA 20 cm radio survey of theAKARIDeep Field South near the South Ecliptic Pole

The results of a deep radio survey at 20 cm wavelength are reported for a region containing the AKARI Deep Field South (ADF-S) near the South Ecliptic Pole (SEP), using the Australia Telescope Compact Array (ATCA). The survey (hereafter referred to as the ATCA-ADFS survey) has 1σ detection limits ranging from 18.7 to 50 μJy beam−1 over an area of ∼1.1 deg2, and ∼2.5 deg2 to lower sensitivity. The observations, data reduction and source count analysis are presented along with a description of the overall scientific objectives, and a catalogue containing 530 radio sources detected with a resolution of 6.2 × 4.9 arcsec. The derived differential source counts show a pronounced excess of sources fainter than ∼1 mJy, consistent with an emerging population of star-forming galaxies. Cross-correlating the radio with AKARI sources and archival data we find 95 cross-matches, with most galaxies having optical R-magnitudes in the range 18–24 mag, similar to that found in other optical deep field identifications, and 52 components lying within 1 arcsec of a radio position in at least one further catalogue (either IR or optical). We have reported redshifts for a sub-sample of our catalogue finding that they vary between galaxies in the local Universe and those having redshifts of up to 0.825. Associating the radio sources with the Spitzer catalogue at 24 μm, we find 173 matches within one Spitzer pixel, of which a small sample of the identifications are clearly radio loud compared to the bulk of the galaxies. The radio luminosity plot and a colour–colour analysis suggest that the majority of the radio sources are in fact luminous star-forming galaxies rather than radio-loud active galactic nuclei (AGN). There are additionally five cross-matches between the Atacama Submillimetre Telescope Experiment (ASTE) or the Balloon-borne Large Aperture Submillimetre Telescope (BLAST) galaxies and radio sources from this survey, two of which are also detected at 90 μm, and 41 cross-matches with submillimetre sources detected in the Herschel Multi-tiered Extragalactic Survey (HerMES) Public Data release.

Radio detection of nebulae around four luminous blue variable stars in the Large Magellanic Cloud

The nebulae associated with four luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC) have been observed at 5.5 and 9 GHz using the Australia Telescope Compact Array, and radio emission has been detected for first time in sources R127, R143, S61 and S119. The radio maps of the nebulae have an angular resolution of ∼1.5 arcsec and a sensitivity of 1.5–3.0 × 10^(−2) mJy beam^(−1) and show a very similar morphology to that observed in Hα. This similarity permits us to assume that the Hα emission is not affected by strong intrinsic extinction due to dust within the nebulae. We estimate the masses of ionized gas in the LBV nebulae and find values consistent with those measured in Galactic LBVs.

The G305 star-forming complex: a wide-area radio survey of ultracompact H ii regions

We present wide-area radio continuum 5.5 and 8.8 GHz (5.5 and 3.4 cm) Australia Telescope Compact Array observations of the complex and rich massive star-forming region G305. The aim of this study is to perform an un-targeted survey of the region in search of the compact radio emission associated with ultra-compact (UC) HII regions. Observations presented here encompass the entire complex and have a maximum resolution of 1:5 1:4 00 and sensitivity of 0:07 mJy beam 1 . By applying a data reduction method that emphasises small-scale structure, we are able to detect 71 compact radio sources distributed throughout the observed field. To explore the nature of these compact radio sources we compare to mid-infrared data and in this way identify 56 background sources, eight stellar radio sources, a single brightrimmed cloud and six candidate UC HII regions. The physical properties of these candidate UC HII regions are determined and reveal five candidates have peak properties consistent with known UC HII regions with source radii ranging from 0.04‐0.1 pc, emission measures from 2.56‐10.3 10 6 pc cm 6 and electron densities of 0.34‐1.03 10 4 cm 3 . We comment on these sites of recent massive star formation within G305 and by comparing to other star formation tracers (masers, NH3, YSOs) build a picture of the star formation history of the region. Using these results we estimate a lower limit to the star formation rate for the region of 0.003 M yr 1 . .

ATLAS, and Wide-Angle Tail Galaxies in ATLAS

Using the Australia Telescope Compact Array (ATCA), ATLAS (Australia Telescope Large Area Survey) is imaging two fields totalling 7 square degrees down to 10 μJy beam − 1 at 1.4 GHz. We have found 6 wide-angle tail galaxies (WATs), 4 of which have sufficient data to identify associated galaxy overdensities. The largest WAT, at a red-shift of 0.22, appears to be associated with an overdensity of galaxies that is spread over an unusually large extent of 12 Mpc, with a velocity range of 4500 km s − 1. Here we present the WATs in ATLAS and discuss the implications of these observations for future large-scale radio surveys such as ASKAP-EMU.