Search

We report on a survey for associated HI 21-cm and OH 18-cm absorption with the Giant Metrewave Radio Telescope at redshifts z = 0.2-0.4. Although the low redshift selection ensures that our targets are below the critical ultra-violet luminosity, which is hypothesised to ionise all of the neutral gas in the host galaxy, we do not obtain any detections in the six sources searched. Analysing these in context of the previous surveys, in addition to the anti-correlation with the ultra-violet luminosity (ionising photon rate), we find a correlation between the strength of the absorption and the blue -- near-infrared colour, as well as the radio-band turnover frequency. We believe that these are due to the photo-ionisation of the neutral gas, an obscured sight-line being more conducive to the presence of cold gas and the compact radio emission being better intercepted by the absorbing gas, maximising the flux coverage, respectively. Regarding the photo-ionisation, the compilation of the previous surveys increases the significance of the critical ionising photon rate, above which all of the gas in the host galaxy is hypothesised to be ionised, to >5 sigma. This reaffirms that this is an ubiquitous effect, which has profound implications for the detection of neutral gas in these objects with the Square Kilometre Array., Accepted by MNRAS

Aim This study aims to assess the prevalence of bifid mandibular canals in a UK population using cone beam computed tomography. Materials and Methods This is a prevalence study of 140 patients (280 sides) referred to a dental hospital in the UK for extraction of a third molar. Canals were classified from cone beam computed tomography images using a novel classification. Results At least one bifid canal was seen in 30.00% (n = 42/140) of patients (95% CI: 26.13–33.87%) and in 18.93% (n = 53/280) of sides (95% CI: 16.59–21.27%). The retromolar canal was the most common variant observed. Conclusions The bifid mandibular canal appears to be a common anatomical variant, of which clinicians should be aware. These variants are relevant to surgery in the retromolar region, dental extraction and implant placement, where damage has the potential to cause bleeding and sensory disturbance.

Gravitational waves have been detected from a binary neutron star merger event, GW170817. The detection of electromagnetic radiation from the same source has shown that the merger occurred in the outskirts of the galaxy NGC 4993, at a distance of 40 megaparsecs from Earth. We report the detection of a counterpart radio source that appears 16 days after the event, allowing us to diagnose the energetics and environment of the merger. The observed radio emission can be explained by either a collimated ultra-relativistic jet viewed off-axis, or a cocoon of mildly relativistic ejecta. Within 100 days of the merger, the radio light curves will distinguish between these models and very long baseline interferometry will have the capability to directly measure the angular velocity and geometry of the debris., Science, in press, 26 pages, DOI:10.1126/science.aap9855

We present a Bayesian Stacking technique to directly measure the HI mass function (HIMF) and its evolution with redshift using galaxies formally below the nominal detection threshold. We generate galaxy samples over several sky areas given an assumed HIMF described by a Schechter function and simulate the HI emission lines with different levels of background noise to test the technique. We use Multinest to constrain the parameters of the HIMF in a broad redshift bin, demonstrating that the HIMF can be accurately reconstructed, using the simulated spectral cube far below the HI mass limit determined by the $5\sigma$ flux-density limit, i.e. down to $M_{\rm HI} = 10^{7.5}$ M$_{\odot}$ over the redshift range $0 < z < 0.55$ for this particular simulation, with a noise level similar to that expected for the MIGHTEE survey. We also find that the constraints on the parameters of the Schechter function, $\phi_{\star}$, $M_\star$ and $\alpha$ can be reliably fit, becoming tighter as the background noise decreases as expected, although the constraints on the redshift evolution are not significantly affected. All the parameters become better constrained as the survey area increases. In summary, we provide an optimal method for estimating the HI mass at cosmological distances that allows us to constrain the HI mass function below the detection threshold in forthcoming HI surveys. This study is a first step towards the measurement of the HIMF at high ($z>0.1$) redshifts., Comment: 17 pages, 11 figures, revised manuscript accepted for publication in MNRAS

We have observed the G23 field of the Galaxy And Mass Assembly (GAMA) survey using the Australian Square Kilometre Array Pathfinder (ASKAP) in its commissioning phase, to validate the performance of the telescope and to characterize the detected galaxy populations. This observation covers $\sim$48 deg$^2$ with synthesized beam of 32.7$^{\prime\prime}$ by 17.8$^{\prime\prime}$ at 936 MHz, and $\sim$39 deg$^2$ with synthesized beam of 15.8$^{\prime\prime}$ by 12.0$^{\prime\prime}$ at 1320 MHz. At both frequencies, the r.m.s. (root-mean-square) noise is $\sim$0.1 mJy/beam. We combine these radio observations with the GAMA galaxy data, which includes spectroscopy of galaxies that are i-band selected with a magnitude limit of 19.2. Wide-field Infrared Survey Explorer (WISE) infrared (IR) photometry is used to determine which galaxies host an active galactic nucleus (AGN). In properties including source counts, mass distributions, and IR vs. radio luminosity relation, the ASKAP detected radio sources behave as expected. Radio galaxies have higher stellar mass and luminosity in IR, optical and UV than other galaxies. We apply optical and IR AGN diagnostics and find that they disagree for $\sim$30% of the galaxies in our sample. We suggest possible causes for the disagreement. Some cases can be explained by optical extinction of the AGN, but for more than half of the cases we do not find a clear explanation. Radio sources are more likely ($\sim$6%) to have an AGN than radio quiet galaxies ($\sim$1%), but the majority of AGN are not detected in radio at this sensitivity., Comment: 26 pages, 22 figures, 6 tables. Accepted for publication in Publications of the Astronomical Society of Australia

With the Australian Square Kilometre Array Pathfinder (ASKAP) we monitored the black hole candidate X-ray binary MAXI J1535--571 over seven epochs from 21 September to 2 October 2017. Using ASKAP observations, we studied the HI absorption spectrum from gas clouds along the line-of-sight and thereby constrained the distance to the source. The maximum negative radial velocities measured from the HI absorption spectra for MAXI J1535--571 and an extragalactic source in the same field of view are $-69\pm4$ km s$^{-1}$ and $-89\pm4$ km s$^{-1}$, respectively. This rules out the far kinematic distance ($9.3^{+0.5}_{-0.6}$ kpc), giving a most likely distance of $4.1^{+0.6}_{-0.5}$ kpc, with a strong upper limit of the tangent point at $6.7^{+0.1}_{-0.2}$ kpc. At our preferred distance, the peak unabsorbed luminosity of MAXI J1535--571 was $>78$ per cent of the Eddington luminosity, and shows that the soft-to-hard spectral state transition occurred at the very low luminosity of 1.2 -- 3.4 $\times$ 10$^{-5}$ times the Eddington luminosity. Finally, this study highlights the capabilities of new wide-field radio telescopes to probe Galactic transient outbursts, by allowing us to observe both a target source and a background comparison source in a single telescope pointing., Revised after favorable referee report from MNRAS Letters

We present a pilot search for variable and transient sources at 1.4 GHz with the Australian Square Kilometre Array Pathfinder (ASKAP). The search was performed in a 30 deg$^{2}$ area centred on the NGC 7232 galaxy group over 8 epochs and observed with a near-daily cadence. The search yielded nine potential variable sources, rejecting the null hypothesis that the flux densities of these sources do not change with 99.9% confidence. These nine sources displayed flux density variations with modulation indices m $\geq 0.1$ above our flux density limit of 1.5 mJy. They are identified to be compact AGN/quasars or galaxies hosting an AGN, whose variability is consistent with refractive interstellar scintillation. We also detect a highly variable source with modulation index m $ > 0.5$ over a time interval of a decade between the Sydney University Molonglo Sky Survey (SUMSS) and our latest ASKAP observations. We find the source to be consistent with the properties of long-term variability of a quasar. No transients were detected on timescales of days and we place an upper limit $��< 0.01$ deg$^{2}$ with 95% confidence for non-detections on near-daily timescales. The future VAST-Wide survey with 36-ASKAP dishes will probe the transient phase space with a similar cadence to our pilot survey, but better sensitivity, and will detect and monitor rarer brighter events., 13 pages, 10 figures. Accepted in MNRAS

Using the Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder (ASKAP BETA), we have carried out the first $z = 0 - 1$ survey for HI and OH absorption towards the gravitationally lensed quasars PKSB1830$-$211 and MGJ0414$+$0534. Although we detected all previously reported intervening systems towards PKSB1830$-$211, in the case of MGJ0414+0534 three systems were not found, indicating that the original identifications may have been confused with radio frequency interference. Given the sensitivity of our data, we find that our detection yield is consistent with the expected frequency of intervening HI systems estimated from previous surveys for 21-cm emission in nearby galaxies and $z \sim 3$ damped Lyman $\alpha$ absorbers. We find spectral variability in the $z = 0.886$ face-on spiral galaxy towards PKSB1830$-$211, from observations undertaken with the Westerbork Synthesis Radio Telescope in 1997/1998 and ASKAP BETA in 2014/2015. The HI equivalent width varies by a few per cent over approximately yearly time-scales. This long-term spectral variability is correlated between the north-east and south-west images of the core, and with the total flux density of the source, implying that it is observationally coupled to intrinsic changes in the quasar. The absence of any detectable variability in the ratio of HI associated with the two core images is in stark contrast to the behaviour previously seen in the molecular lines. We therefore infer that coherent opaque HI structures in this galaxy are larger than the parsec-scale molecular clouds found at mm-wavelengths., Comment: 19 pages, 11 figures, published in MNRAS

We present a statistical method for measuring the average HI spin temperature in distant galaxies using the expected detection yields from future wide-field 21cm absorption surveys. As a demonstrative case study we consider a simulated all-southern-sky survey of 2-h per pointing with the Australian Square Kilometre Array Pathfinder for intervening HI absorbers at intermediate cosmological redshifts between $z = 0.4$ and $1$. For example, if such a survey yielded $1000$ absorbers we would infer a harmonic-mean spin temperature of $\overline{T}_\mathrm{spin} \sim 100$K for the population of damped Lyman $\alpha$ (DLAs) absorbers at these redshifts, indicating that more than $50$ per cent of the neutral gas in these systems is in a cold neutral medium (CNM). Conversely, a lower yield of only 100 detections would imply $\overline{T}_\mathrm{spin} \sim 1000$K and a CNM fraction less than $10$ per cent. We propose that this method can be used to provide independent verification of the spin temperature evolution reported in recent 21cm surveys of known DLAs at high redshift and for measuring the spin temperature at intermediate redshifts below $z \approx 1.7$, where the Lyman-$\alpha$ line is inaccessible using ground-based observatories. Increasingly more sensitive and larger surveys with the Square Kilometre Array should provide stronger statistical constraints on the average spin temperature. However, these will ultimately be limited by the accuracy to which we can determine the HI column density frequency distribution, the covering factor and the redshift distribution of the background radio source population., Comment: 11 pages, 9 figures, 1 table. Proof corrected version

Since January 2017, the Commensal Real-time ASKAP Fast Transients survey (CRAFT) has been utilising commissioning antennas of the Australian SKA Pathfinder (ASKAP) to survey for fast radio bursts (FRBs) in fly's eye mode. This is the first extensive astronomical survey using phased array feeds (PAFs), and a total of 20 FRBs have been reported. Here we present a calculation of the sensitivity and total exposure of this survey, using the pulsars B1641-45 (J1644-4559) and B0833-45 (J0835-4510, i.e.\ Vela) as calibrators. The design of the survey allows us to benchmark effects due to PAF beamshape, antenna-dependent system noise, radio-frequency interference, and fluctuations during commissioning on timescales from one hour to a year. Observation time, solid-angle, and search efficiency are calculated as a function of FRB fluence threshold. Using this metric, effective survey exposures and sensitivities are calculated as a function of the source counts distribution. The implied FRB rate is significantly lower than the $37$\,sky$^{-1}$\,day$^{-1}$ calculated using nominal exposures and sensitivities for this same sample by \citet{craft_nature}. At the Euclidean power-law index of $-1.5$, the rate is $10.7_{-1.8}^{+2.7}\,{\rm (sys)} \, \pm \, 3\,{\rm (stat)}$\,sky$^{-1}$\,day$^{-1}$ above a threshold of $57\pm6\,{\rm (sys)}$\,Jy\,ms, while for the best-fit index for this sample of $-2.1$, it is $16.6_{-1.5}^{+1.9} \,{\rm (sys)}\, \pm 4.7\,{\rm (stat)}$\,sky$^{-1}$\,day$^{-1}$ above a threshold of $41.6\pm1.5\,{\rm (sys)}$\,Jy\,ms. This strongly suggests that these calculations be performed for other FRB-hunting experiments, allowing meaningful comparisons to be made between them., Comment: 21 pages, 15 figures, 2 tables, accepted for publication in PASA

We are just starting to understand the physical processes driving the dramatic change in cosmic star-formation rate between $z\sim 2$ and the present day. A quantity directly linked to star formation is the molecular gas density, which should be measured through independent methods to explore variations due to cosmic variance and systematic uncertainties. We use intervening CO absorption lines in the spectra of mm-bright background sources to provide a census of the molecular gas mass density of the Universe. The data used in this work are taken from ALMACAL, a wide and deep survey utilizing the ALMA calibrator archive. While we report multiple Galactic absorption lines and one intrinsic absorber, no extragalactic intervening molecular absorbers are detected. However, thanks to the large redshift path surveyed ($\Delta z=182$), we provide constraints on the molecular column density distribution function beyond $z\sim 0$. In addition, we probe column densities of N(H$_2$) > 10$^{16}$ atoms~cm$^{-2}$, five orders of magnitude lower than in previous studies. We use the cosmological hydrodynamical simulation IllustrisTNG to show that our upper limits of $\rho ({\rm H}_2)\lesssim 10^{8.3} \text{M}_{\odot} \text{Mpc}^{-3}$ at $0 < z \leq 1.7$ already provide new constraints on current theoretical predictions of the cold molecular phase of the gas. These results are in agreement with recent CO emission-line surveys and are complementary to those studies. The combined constraints indicate that the present decrease of the cosmic star-formation rate history is consistent with an increasing depletion of molecular gas in galaxies compared to $z\sim 2$., Comment: 11 pages, 10 figures, 2 tables, accepted for publication in MNRAS

This paper reports on the atomic hydrogen gas (HI) observations of the spiral galaxy NGC 1566 using the newly commissioned Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. We measure an integrated HI flux density of $180.2$ Jy km s$^{-1}$ emanating from this galaxy, which translates to an HI mass of $1.94\times10^{10}$M$_\circ$ at an assumed distance of $21.3$ Mpc. Our observations show that NGC 1566 has an asymmetric and mildly warped HI disc. The HI-to-stellar mass fraction of NGC 1566 is $0.29$, which is high in comparison with galaxies that have the same stellar mass ($10^{10.8}$M$_\circ$). We also derive the rotation curve of this galaxy to a radius of $50$ kpc and fit different mass models to it. The NFW, Burkert and pseudo-isothermal dark matter halo profiles fit the observed rotation curve reasonably well and recover dark matter fractions of $0.62$, $0.58$ and $0.66$, respectively. Down to the column density sensitivity of our observations ($N_{HI} = 3.7\times10^{19}$ cm$^{-2}$), we detect no HI clouds connected to, or in the nearby vicinity of, the HI disc of NGC 1566 nor nearby interacting systems. We conclude that, based on a simple analytic model, ram pressure interactions with the IGM can affect the HI disc of NGC 1566 and is possibly the reason for the asymmetries seen in the HI morphology of NGC 1566., Comment: Accepted for publication in MNRAS

Objectives Identify splatter/aerosol distribution from dental procedures in an open plan clinic and explore aerosol settling time after dental procedures. Methods In two experimental designs using simulated dental procedures on a mannequin, fluorescein dye was introduced: (1) into the irrigation system of an air-turbine handpiece; (2) into the mannequin's mouth. Filter papers were placed in an open plan clinic to collect fluorescein. An 8-metre diameter rig was used to investigate aerosol settling time. Analysis was by fluorescence photography and spectrofluorometry. Results Contamination distribution varied across the clinic depending on conditions. Unmitigated procedures have the potential to deposit contamination at large distances. Medium volume dental suction (159 L/min air) reduced contamination in the procedural bay by 53%, and in other areas by 81-83%. Low volume suction (40 L/min air) was similar. Cross-ventilation reduced contamination in adjacent and distant areas by 80-89%. In the most realistic model (fluorescein in mouth, medium volume suction), samples in distant bays (≥5 m head-to-head chair distance) gave very low or zero readings (< 0.0016% of the fluorescein used during the procedure). Almost all (99.99%) of the splatter detected was retained within the procedural bay/walkway. After 10 min, very little additional aerosol settled. Conclusions Cross-infection risk from dental procedures in an open plan clinic appears small when bays are ≥ 5 m apart. Dilution effects from instrument water spray were observed, and dental suction is of benefit. Most settled aerosol is detected within 10 min indicating environmental cleaning may be appropriate after this. Clinical Significance: Aerosols produced by dental procedures have the potential to contaminate distant sites and the majority of settled aerosol is detectable after 10 min. Dental suction and ventilation have a substantial beneficial effect. Contamination is likely to be minimal in open plan clinics at distances of 5 m or more.

We examine the processes triggering star formation and Active Galactic Nucleus (AGN) activity in a sample of 25 low redshift ($z10^7$ K) brightness temperature required for an mJIVE-20 detection allows us to unambiguously identify the radio AGN in our sample. We find three such objects. Our VLBI AGN identifications are classified as Seyferts or LINERs in narrow line optical diagnostic plots; mid-infrared colours of our targets and the comparison of H$��$ star formation rates with integrated radio luminosity are also consistent with the VLBI identifications. We reconstruct star formation histories in our galaxies using optical and UV photometry, and find that these radio AGN are not triggered promptly in the merger process, consistent with previous findings for non-VLBI samples of radio AGN. This delay can significantly limit the efficiency of feedback by radio AGN triggered in galaxy mergers. We find that radio AGN hosts have lower star formation rates than non-AGN radio-selected galaxies at the same starburst age. Conventional and VLBI radio imaging shows these AGN to be compact on arcsecond scales. Our modeling suggests that the actual sizes of AGN-inflated radio lobes may be much larger than this, but these are too faint to be detected in existing observations. Deep radio imaging is required to map out the true extent of the AGN, and to determine whether the low star formation rates in radio AGN hosts are a result of the special conditions required for radio jet triggering, or the effect of AGN feedback., 16 pages, 9 figures. Accepted for publication in MNRAS

We present the results of a survey for intervening 21cm HI absorption in a sample of 10 nearby, gas-rich galaxies selected from the HI Parkes All-Sky Survey (HIPASS). This follows the six HIPASS galaxies searched in previous work and completes our full sample. In this paper we searched for absorption along 17 sightlines with impact parameters between 6 and 46 kpc, making one new detection. We also obtained simultaneous HI emission-line data, allowing us to directly relate the absorption-line detection rate to the HI distribution. From this we find the majority of the non-detections in the current sample are because sightline does not intersect the HI disc of the galaxy at sufficiently high column density, but that source structure is also an important factor. The detected absorption-line arises in the galaxy NGC 5156 ($z = 0.01$) at an impact parameter of 19 kpc. The line is deep and narrow with an integrated optical depth of 0.82 km s$^{-1}$. High resolution Australia Telescope Compact Array (ATCA) images at 5 and 8 GHz reveal that the background source is resolved into two components with a separation of 2.6 arcsec (500 pc at the redshift of the galaxy), with the absorption likely occurring against a single component. We estimate that the ratio of the spin temperature and covering factor, $T_{\mathrm{S}}/f$, is approximately 950 K in the outer disc of NGC 5156, but further observations using VLBI would allow us to accurately measure the covering factor and spin temperature of the gas., 31 pages, 11 figures

At present neutral atomic hydrogen (H I) gas in galaxies at redshifts above z ∼ 0.3 (the extent of 21 cm emission surveys in individual galaxies) and below z ∼ 1.7 (where the Lyman-α line is not observable with ground-based telescopes) has remained largely unexplored. The advent of precursor telescopes to the Square Kilometre Array will allow us to conduct the first systematic radio-selected 21 cm absorption surveys for H I over these redshifts. While H I absorption is a tracer of the reservoir of cold neutral gas in galaxies available for star formation, it can also be used to reveal the extreme kinematics associated with jet-driven neutral outflows in radio-loud active galactic nuclei. Using the six-antenna Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder, we have demonstrated that in a single frequency tuning we can detect H I absorption over a broad range of redshifts between z = 0.4 and 1.0. As part of our early science and commissioning program, we are now carrying out a search for absorption towards a sample of the brightest GPS and CSS sources in the southern sky. These intrinsically compact sources present us with an opportunity to study the circumnuclear region of recently re-started radio galaxies, in some cases showing direct evidence of mechanical feedback through jetdriven outflows. With the sensitivity of the full ASKAP array we will be able to study the kinematics of atomic gas in a few thousand radio galaxies, testing models of radio jet feedback well beyond the nearby Universe. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Feedback from massive stars plays a critical role in the evolution of the Universe by driving powerful outflows from galaxies that enrich the intergalactic medium and regulate star formation. An important source of outflows may be the most numerous galaxies in the Universe: dwarf galaxies. With small gravitational potential wells, these galaxies easily lose their star-forming material in the presence of intense stellar feedback. Here, we show that the nearby dwarf galaxy, the Small Magellanic Cloud (SMC), has atomic hydrogen outflows extending at least 2 kiloparsecs (kpc) from the star-forming bar of the galaxy. The outflows are cold, $T, Published in Nature Astronomy, 29 October 2018, http://dx.doi.org/10.1038/s41550-018-0608-8

We present Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early science results from the Australian Square Kilometre Array Pathfinder (ASKAP) observations of the NGC 7162 galaxy group. We use archival HIPASS and Australia Telescope Compact Array (ATCA) observations of this group to validate the new ASKAP data and the data reduction pipeline ASKAPsoft. We detect six galaxies in the neutral hydrogen (HI) 21-cm line, expanding the NGC 7162 group membership from four to seven galaxies. Two of the new detections are also the first HI detections of the dwarf galaxies, AM 2159-434 and GALEXASC J220338.65-431128.7, for which we have measured velocities of $cz=2558$ and $cz=2727$ km s$^{-1}$, respectively. We confirm that there is extended HI emission around NGC 7162 possibly due to past interactions in the group as indicated by the $40^{\circ}$ offset between the kinematic and morphological major axes for NGC 7162A, and its HI richness. Taking advantage of the increased resolution (factor of $\sim1.5$) of the ASKAP data over archival ATCA observations, we fit a tilted ring model and use envelope tracing to determine the galaxies' rotation curves. Using these we estimate the dynamical masses and find, as expected, high dark matter fractions of $f_{\mathrm{DM}}\sim0.81-0.95$ for all group members. The ASKAP data are publicly available., 20 pages, 11 figures, accepted for publication in MNRAS

Cold neutral gas is a key ingredient for growing the stellar and central black hole mass in galaxies throughout cosmic history. We have used the Atacama Large Millimetre Array (ALMA) to detect a rare example of redshifted $^{12}$CO(2-1) absorption in PKS B1740-517, a young ($t \sim 1.6 \times 10^{3}$ yr) and luminous ($L_{\rm 5 GHz} \sim 6.6 \times 10^{43}$ erg s$^{-1}$ ) radio galaxy at $z = 0.44$ that is undergoing a tidal interaction with at least one lower-mass companion. The coincident HI 21-cm and molecular absorption have very similar line profiles and reveal a reservoir of cold gas ($M_{\rm gas} \sim 10^{7} - 10^{8}$ M$_{\odot}$), likely distributed in a disc or ring within a few kiloparsecs of the nucleus. A separate HI component is kinematically distinct and has a very narrow line width ($\Delta{v}_{\rm FWHM} \lesssim 5$ km s$^{-1}$), consistent with a single diffuse cloud of cold ($T_{\rm k} \sim 100$ K) atomic gas. The $^{12}$CO(2-1) absorption is not associated with this component, which suggests that the cloud is either much smaller than 100 pc along our sight-line and/or located in low-metallicity gas that was possibly tidally stripped from the companion. We argue that the gas reservoir in PKS B1740-517 may have accreted onto the host galaxy $\sim$50 Myr before the young radio AGN was triggered, but has only recently reached the nucleus. This is consistent with the paradigm that powerful luminous radio galaxies are triggered by minor mergers and interactions with low-mass satellites and represent a brief, possibly recurrent, active phase in the life cycle of massive early type galaxies., Comment: 15 pages, 7 figures, accepted for publication in MNRAS

Despite considerable efforts over the past decade, only 34 fast radio bursts—intense bursts of radio emission from beyond our Galaxy—have been reported1,2. Attempts to understand the population as a whole have been hindered by the highly heterogeneous nature of the searches, which have been conducted with telescopes of different sensitivities, at a range of radio frequencies, and in environments corrupted by different levels of radio-frequency interference from human activity. Searches have been further complicated by uncertain burst positions and brightnesses—a consequence of the transient nature of the sources and the poor angular resolution of the detecting instruments. The discovery of repeating bursts from one source3, and its subsequent localization4 to a dwarf galaxy at a distance of 3.7 billion light years, confirmed that the population of fast radio bursts is located at cosmological distances. However, the nature of the emission remains elusive. Here we report a well controlled, wide-field radio survey for these bursts. We found 20, none of which repeated during follow-up observations between 185–1,097 hours after the initial detections. The sample includes both the nearest and the most energetic bursts detected so far. The survey demonstrates that there is a relationship between burst dispersion and brightness and that the high-fluence bursts are the nearby analogues of the more distant events found in higher-sensitivity, narrower-field surveys5.

The circumgalactic medium (CGM) of the massive Spiderweb Galaxy, a conglomerate of merging proto-cluster galaxies at z=2.2, forms an enriched interface where feedback and recycling act on accreted gas. This is shown by observations of [CI], CO(1-0) and CO(4-3) performed with the Atacama Large Millimeter Array (ALMA) and Australia Telescope Compact Array (ATCA). [CI] and CO(4-3) are detected across ~50 kpc, following the distribution of previously detected low-surface-brightness CO(1-0) across the CGM. This confirms our previous results on the presence of a cold molecular halo. The central radio galaxy MRC1138-262 shows a very high global $L'_{\rm CO(4-3)}$/$L'_{\rm CO(1-0)}$ ~ 1, suggesting that mechanisms other than FUV-heating by star formation prevail at the heart of the Spiderweb Galaxy. Contrary, the CGM has $L'_{\rm CO(4-3)}$/$L'_{\rm CO(1-0)}$ and $L'_{\rm [CI]}$/$L'_{\rm CO(1-0)}$ similar to the ISM of five galaxies in the wider proto-cluster, and its carbon abundance, $X_{\rm [CI]}$/$X_{\rm H2}$, resembles that of the Milky Way and starforming galaxies. The molecular CGM is thus metal-rich and not diffuse, confirming a link between the cold gas and in-situ star formation. Thus, the Spiderweb Galaxy grows not directly through accretion of gas from the cosmic web, but from recycled gas in the GCM., Accepted for publication as a Letter in MNRAS (5 pages, 4 figures)

Gas-rich minor mergers contribute significantly to the gas reservoir of early-type galaxies (ETGs) at low redshift, yet the star formation efficiency (SFE; the star formation rate divided by the molecular gas mass) appears to be strongly suppressed following some of these events, in contrast to the more well-known merger-driven starbursts. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of six ETGs, which have each recently undergone a gas-rich minor merger, as evidenced by their disturbed stellar morphologies. These galaxies were selected because they exhibit extremely low SFEs. We use the resolving power of ALMA to study the morphology and kinematics of the molecular gas. The majority of our galaxies exhibit spatial and kinematical irregularities, such as detached gas clouds, warps, and other asymmetries. These asymmetries support the interpretation that the suppression of the SFE is caused by dynamical effects stabilizing the gas against gravitational collapse. Through kinematic modelling we derive high velocity dispersions and Toomre Q stability parameters for the gas, but caution that such measurements in edge-on galaxies suffer from degeneracies. We estimate merger ages to be about 100~Myr based on the observed disturbances in the gas distribution. Furthermore, we determine that these galaxies lie, on average, two orders of magnitude below the Kennicutt-Schmidt relation for star-forming galaxies as well as below the relation for relaxed ETGs. We discuss potential dynamical processes responsible for this strong suppression of star formation surface density at fixed molecular gas surface density., Comment: Accepted for publication in MNRAS

We present the results of a targeted search for intervening HI absorption in six nearby, gas-rich galaxies using the Australia Telescope Compact Array (ATCA). The sightlines searched have impact parameters of 10-20 kpc. By targeting nearby galaxies we are also able to map their HI emission, allowing us to directly relate the absorption-line detection rate to the extended HI distribution. The continuum sightlines intersect the HI disk in four of the six galaxies, but no intervening absorption was detected. Of these four galaxies, we find that three of the non-detections are the result of the background source being too faint. In the fourth case we find that the ratio of the spin temperature to the covering factor ($T_{\mathrm{S}}/f$) must be much higher than expected ($\gtrsim$5700 K) in order to explain the non-detection. We discuss how the structure of the background continuum sources may have affected the detection rate of HI absorption in our sample, and the possible implications for future surveys. Future work including an expanded sample, and VLBI observations, would allow us to better investigate the expected detection rate, and influence of background source structure, on the results of future surveys., 18 pages, 8 figures

Cone Beam Computed Tomography (CBCT) has recently seen an expansion in use, however there are few robust, evidence-based guidelines to inform practitioners. This article reports the case of a large dentigerous cyst in the maxilla affecting the eruption of multiple teeth, considers the use of CBCT in the management of such lesions, and discusses guidelines on the use of CBCT in dentistry. CPD/Clinical Relevance: As CBCT use increases it is important that practitioners understand the guidelines surrounding its use. Due to the prevalence of dentigerous cysts, it is likely that they will be encountered clinically, and it is important that clinicians referring patients with such lesions are familiar with the principles of managing them.

We report the results of a survey for HI 21-cm absorption at redshifts of z > 2.6 in a new sample of radio sources with the Green Bank and Giant Metrewave Radio Telescopes. From a total of 25 targets, we report zero detections in the 16 for which optical depth limits could be obtained. Based upon the detection rate for z > 0.1 associated absorption, we would expect approximately four detections. Of the 11 which have previously not been searched, there is sufficient source-frame optical/ultra-violet photometry to determine the ionising photon rate for four. Adding these to the literature, the hypothesis that there is a critical rate of logQ = 56 ionising photons per second is now significant at ~7 sigma. This reaffirms our assertion that searching z > 3 active galaxies for which optical redshifts are available selects sources in which the ultra-violet luminosity is sufficient to ionise all of the neutral gas in the host galaxy., Accepted by MNRAS

HI absorption studies yield information on both AGN feeding and feedback processes. This AGN activity interacts with the neutral gas in compact radio sources, which are believed to represent the young or recently re-triggered AGN population. We present the results of a survey for HI absorption in a sample of 66 compact radio sources at 0.040 < z < 0.096 with the Australia Telescope Compact Array. In total, we obtained seven detections, five of which are new, with a large range of peak optical depths (3% to 87%). Of the detections, 71% exhibit asymmetric, broad ($��{v}_{\mathrm{FWHM}}$ > 100 km s$^{-1}$) features, indicative of disturbed gas kinematics. Such broad, shallow and offset features are also found within low-excitation radio galaxies which is attributed to disturbed circumnuclear gas, consistent with early-type galaxies typically devoid of a gas-rich disk. Comparing mid-infrared colours of our galaxies with HI detections indicates that narrow and deep absorption features are preferentially found in late-type and high-excitation radio galaxies in our sample. These features are attributed to gas in galactic disks. By combining XMM-Newton archival data with 21-cm data, we find support that absorbed X-ray sources may be good tracers of HI content within the host galaxy. This sample extends previous HI surveys in compact radio galaxies to lower radio luminosities and provides a basis for future work exploring the higher redshift universe., 23 pages, 9 figures and 7 tables; accepted for publication in MNRAS

Amtrak launched free Wi-Fi internet service (“AmtrakConnect”) on all trains of the California Capitol Corridor route (CC) on November 28, 2011. In March 2012, an onboard survey was conducted to evaluate the impact of the Wi-Fi service on ridership. We develop descriptive statistics and estimate a linear regression model of the impact of Wi-Fi on passengers’ trip frequency. As higher-frequency riders are overrepresented in the original sample, we weight cases to reflect the distribution of passengers, rather than person-trips, more accurately. We segment the linear regression model for three groups of travelers, based on their ridership frequency, to better understand the impact of selected variables on the expected number of trips in 2012. Several conventional factors (trip frequency in 2011, trip purpose, station-to-station distance and employment) as well as Wi-Fi have some impact on the self-reported projected trip frequency in 2012. Using the estimated parameters from the model, the expected number of trips on CC trains for 2012 is 2.7 % higher than it would have been without free Wi-Fi. In particular, new riders expect to make 8.6 % more trips than if Wi-Fi were not available, while the expected number of trips made by lower-frequency continuing riders (those using CC less than once a week in 2011) and higher-frequency continuing riders (those using CC once a week or more in 2011) increase by 6.2 and 1.0 %, respectively.

Using archival data from the HI Parkes All Sky Survey (HIPASS) we have searched for 21 cm line absorption in 204 nearby radio and star-forming galaxies with continuum flux densities greater than $S_{1.4} \approx 250$ mJy within the redshift range $0 < cz < 12000$ km s$^{-1}$. By applying a detection method based on Bayesian model comparison, we successfully detect and model absorption against the radio-loud nuclei of four galaxies, of which the Seyfert 2 galaxy 2MASX J130804201-2422581 was previously unknown. All four detections were achieved against compact radio sources, which include three active galactic nuclei (AGNs) and a nuclear starburst, exhibiting high dust and molecular gas content. Our results are consistent with the detection rate achieved by the recent ALFALFA (Arecibo Legacy Fast Arecibo L-band Feed Array) HI absorption pilot survey by Darling et al. and we predict that the full ALFALFA survey should yield more than three to four times as many detections as we have achieved here. Furthermore, we predict that future all-sky surveys on the Square Kilometre Array precursor telescopes will be able to detect such strong absorption systems associated with type 2 AGNs at much higher redshifts, providing potential targets for detection of H$_{2}$O megamaser emission at cosmological redshifts., 23 pages, 16 figures, 5 tables; published in MNRAS

Compositional analyses were undertaken to evaluate the hypothesis that Shivwits Ware pottery found in southern Nevada was not produced in that area but, instead, manufactured on the Shivwits Plateau. The evidence supports this hypothesis and indicates that large quantities of Shivwits Ware jars moved through a distribution system linking the upland areas of the western Arizona Strip with the lowlands of southeastern Nevada. This long-distance movement of utilitarian pottery is unusual for precontact North America, in that it occurred in the apparent absence of any centralized distribution mechanisms and between what would have been small, kin-based communities. The nature and the causes for the development of this distribution system are discussed.

We report the discovery of new, high-velocity narrow-line components of the OH megamaser in IRAS 20100-4156. Results from the Australian Square Kilometre Array Pathfinder (ASKAP)'s Boolardy Engineering Test Array (BETA) and the Australia Telescope Compact Array (ATCA) provide two independent measurements of the OH megamaser spectrum. We found evidence for OH megamaser clumps at $-$409 and $-$562 km/s (blue-shifted) from the systemic velocity of the galaxy, in addition to the lines previously known. The presence of such high velocities in the molecular emission from IRAS 20100$-$4156 could be explained by a ~50 pc molecular ring enclosing an approximately 3.8 billion solar mass black hole. We also discuss two alternatives, i.e. that the narrow-line masers are dynamically coupled to the wind driven by the active galactic nucleus or they are associated with two separate galactic nuclei. The comparison between the BETA and ATCA spectra provides another scientific verification of ASKAP's BETA. Our data, combined with previous measurements of the source enabled us to study the variability of the source over a twenty-six year period. The flux density of the brightest OH maser components has reduced by more than a factor of two between 1988 and 2015, whereas a secondary narrow-line component has more than doubled in the same time. Plans for high-resolution VLBI follow-up of this source are discussed, as are prospects for discovering new OH megamasers during the ASKAP early science program., Comment: Accepted to MNRAS. Seven pages, three figures

By combining the data from surveys for HI 21-cm absorption at various impact parameters in near-by galaxies, we report an anti-correlation between the 21-cm absorption strength (velocity integrated optical depth) and the impact parameter. Also, by combining the 21-cm absorption strength with that of the emission, giving the neutral hydrogen column density, we find no evidence that the spin temperature of the gas (degenerate with the covering factor) varies significantly across the disk. This is consistent with the uniformity of spin temperature measured across the Galactic disk. Furthermore, comparison with the Galactic distribution suggests that intervening 21-cm absorption preferentially arises in disks of high inclinations (near face-on). We also investigate the hypothesis that 21-cm absorption is favourably detected towards compact radio sources. Although there is insufficient data to determine whether there is a higher detection rate towards quasar, rather than radio galaxy, sight-lines, the 21-cm detections intervene objects with a mean turnover frequency of 5 x 10^8 Hz, compared to 1 x 10^8 Hz for the non-detections. Since the turnover frequency is anti-correlated with radio source size, this does indicate a preferential bias for detection towards compact background radio sources., Comment: 8 pages accepted by MNRAS

We use observations from the Boolardy Engineering Test Array (BETA) of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to search for transient radio sources in the field around the intermittent pulsar PSR J1107-5907. The pulsar is thought to switch between an "off" state in which no emission is detectable, a weak state and a strong state. We ran three independent transient detection pipelines on two-minute snapshot images from a 13 hour BETA observation in order to 1) study the emission from the pulsar, 2) search for other transient emission from elsewhere in the image and 3) to compare the results from the different transient detection pipelines. The pulsar was easily detected as a transient source and, over the course of the observations, it switched into the strong state three times giving a typical timescale between the strong emission states of 3.7 hours. After the first switch it remained in the strong state for almost 40 minutes. The other strong states lasted less than 4 minutes. The second state change was confirmed using observations with the Parkes radio telescope. No other transient events were found and we place constraints on the surface density of such events on these timescales. The high sensitivity Parkes observations enabled us to detect individual bright pulses during the weak state and to study the strong state over a wide observing band. We conclude by showing that future transient surveys with ASKAP will have the potential to probe the intermittent pulsar population., Comment: Accepted by MNRAS

We present the results of a survey for HI 21-cm and OH 18-cm absorption in seven strong CO emitters at z > 3. Despite reaching limits comparable to those required to detect 21-cm absorption at lower redshifts, we do not detect either transition in any of the objects searched. We believe that this is due to the high redshift selection causing all of our targets to have ultra-violet luminosities above the critical value, where all of the atomic gas in the host galaxy disk is suspected to be ionised. However, not only are all of our targets bright in CO emission, but detection of CO above the critical UV luminosity is generally not uncommon. This suggests that the molecular gas is shielded from the radiation or is physically remote from the source of the continuum emission, as it appears to be from CO observations of high redshift radio galaxies., Comment: 12 pages, accepted by MNRAS

The Boolardy Engineering Test Array is a 6 x 12 m dish interferometer and the prototype of the Australian Square Kilometre Array Pathfinder (ASKAP), equipped with the first generation of ASKAP's phased array feed (PAF) receivers. These facilitate rapid wide-area imaging via the deployment of simultaneous multiple beams within a 30 square degree field of view. By cycling the array through 12 interleaved pointing positions and using 9 digitally formed beams we effectively mimic a traditional 1 hour x 108 pointing survey, covering 150 square degrees over 711 - 1015 MHz in 12 hours of observing time. Three such observations were executed over the course of a week. We verify the full bandwidth continuum imaging performance and stability of the system via self-consistency checks and comparisons to existing radio data. The combined three epoch image has arcminute resolution and a 1-sigma thermal noise level of 375 micro-Jy per beam, although the effective noise is a factor 3 higher due to residual sidelobe confusion. From this we derive a catalogue of 3,722 discrete radio components, using the 35 percent fractional bandwidth to measure in-band spectral indices for 1,037 of them. A search for transient events reveals one significantly variable source within the survey area. The survey covers approximately two-thirds of the Spitzer South Pole Telescope Deep Field. This pilot project demonstrates the viability and potential of using PAFs to rapidly and accurately survey the sky at radio wavelengths., 20 pages, 13 figures, 4 tables. Accepted for publication in MNRAS

The star-forming reservoir in the distant Universe can be detected through HI 21-cm absorption arising from either cool gas associated with a radio source or from within a galaxy intervening the sight-line to the continuum source. In order to test whether the nature of the absorber can be predicted from the profile shape, we have compiled and analysed all of the known redshifted (z > 0.1) HI 21-cm absorption profiles. Although between individual spectra there is too much variation to assign a typical spectral profile, we confirm that associated absorption profiles are on average, wider than their intervening counterparts. It is widely hypothesised that this is due to high velocity nuclear gas feeding the central engine, absent in the more quiescent intervening absorbers. Modelling the column density distribution of the mean associated and intervening spectra, we confirm that the additional low optical depth, wide dispersion component, typical of associated absorbers, arises from gas within the inner parsec. With regard to the potential of predicting the absorber type in the absence of optical spectroscopy, we have implemented machine learning techniques to the 55 associated and 43 intervening spectra, with each of the tested models giving a >80% accuracy in the prediction of the absorber type. Given the impracticability of follow-up optical spectroscopy of the large number of 21-cm detections expected from the next generation of large radio telescopes, this could provide a powerful new technique with which to determine the nature of the absorbing galaxy., Accepted by MNRAS

The largest galaxies in the Universe reside in galaxy clusters. Using sensitive observations of carbon-monoxide, we show that the Spiderweb Galaxy -a massive galaxy in a distant protocluster- is forming from a large reservoir of molecular gas. Most of this molecular gas lies between the protocluster galaxies and has low velocity dispersion, indicating that it is part of an enriched inter-galactic medium. This may constitute the reservoir of gas that fuels the widespread star formation seen in earlier ultraviolet observations of the Spiderweb Galaxy. Our results support the notion that giant galaxies in clusters formed from extended regions of recycled gas at high redshift., Comment: Published in Science on 2 Dec 2016 (accepted 21 Oct 2016), 20 pages, 5 figures, 3 tables. Contains minor copy-editing differences with published version

 Premise of the study: Molecular studies have shown that multiple origins of polyploid taxa are the rule rather than the exception. To understand the distribution and ecology of polyploid species and the evolutionary signifi cance of polyploidy in general, it is important to delineate these independently derived lineages as accurately as possible. Although gene fl ow among polyploid lineages and backcrossing to their diploid parents often confound this process, such post origin gene fl ow is very infrequent in asexual polyploids. In this study, we estimate the number of independent origins of the apomictic allopolyploid fern Astrolepis integerrima , a morphologically heterogeneous species most common in the southwestern United States and Mexico, with outlying populations in the southeastern United States and the Caribbean.  Methods: Plastid DNA sequence and AFLP data were obtained from 33 A. integerrima individuals. Phylogenetic analysis of the sequence data and multidimensional clustering of the AFLP data were used to identify independently derived lineages.  Key results: Analysis of the two datasets identifi ed 10 genetic groups within the 33 analyzed samples. These groups suggest a minimum of 10 origins of A. integerrima in the northern portion of its range, with both putative parents functioning as maternal donors, both supplying unreduced gametes, and both contributing a signifi cant portion of their genetic diversity to the hybrids.  Conclusions: Our results highlight the extreme cryptic genetic diversity and systematic complexity that can underlie a single polyploid taxon.

This article explores how increasing demands for domestic energy resources during the 1970s threatened the survival of American Indian tribes, leading to an impassioned indigenous movement to protect reservation resources and change federal law to increase tribal sovereignty. Beginning with a close examination of the specific reasons why the Northern Cheyenne and Crow resisted potentially lucrative energy development, the investigation follows a broadening national movement to equip tribes with the tools necessary to manage their own affairs. In the face of intense pressure to develop energy resources, American Indians reclaimed control over their reservations and forced changes in federal law that provided the fullest expression of tribal sovereignty since the nineteenth century.

We present results from a search for 21 cm associated HI absorption in a sample of 29 radio sources selected from the Australia Telescope 20 GHz survey. Observations were conducted using the Australia Telescope Compact Array Broadband Backend, with which we can simultaneously look for 21 cm absorption in a redshift range of 0.04 103 km/s . Using this technique we detect two new absorbers and a third, previously known, yielding a 10 per cent detection rate. Of the detections, the spectral-line profiles are consistent with the theory that we are seeing different orientations of the absorbing gas, in both the host galaxy and circumnuclear disc, with respect to our line-of-sight to the source. In order to spatially resolve the spectral-line components in the two new detections, and so verify this conclusion, we require further high-resolution 21 cm observations (~0.01 arcsec) using very long baseline interferometry.

The large spectral bandwidth and wide field of view of the Australian SKA Pathfinder radio telescope will open up a completely new parameter space for large extragalactic HI surveys. Here we focus on identifying and parametrising HI absorption lines which occur in the line of sight towards strong radio continuum sources. We have developed a method for simultaneously finding and fitting HI absorption lines in radio data by using multi-nested sampling, a Bayesian Monte Carlo algorithm. The method is tested on a simulated ASKAP data cube, and is shown to be reliable at detecting absorption lines in low signal-to-noise data without the need to smooth or alter the data. Estimation of the local Bayesian evidence statistic provides a quantitative criterion for assigning significance to a detection and selecting between competing analytical line-profile models., 8 pages, 5 figures and 1 table; accepted for publication in PASA

We describe an upgrade to the Cosmic Background Imager instrument to increase its surface brightness sensitivity at small angular scales. The upgrade consisted of replacing the thirteen 0.9-m antennas with 1.4-m antennas incorporating a novel combination of design features, which provided excellent sidelobe and spillover performance for low manufacturing cost. Off-the-shelf spun primaries were used, and the secondary mirrors were oversized and shaped relative to a standard Cassegrain in order to provide an optimum compromise between aperture efficiency and low spillover lobes. Low-order distortions in the primary mirrors were compensated for by custom machining of the secondary mirrors. The secondaries were supported on a transparent dielectric foam cone to minimize scattering. The antennas were tested in the complete instrument, and the beam shape and spillover noise contributions were as expected. We demonstrate the performance of the telescope and the inter-calibration with the previous system using observations of the Sunyaev-Zel'dovich effect in the cluster Abell 1689. The enhanced instrument has been used to study the cosmic microwave background, the Sunyaev-Zel'dovich effect and diffuse Galactic emission.

The diffuse cm-wave IR-correlated signal, the "anomalous" CMB foreground, is thought to arise in the dust in cirrus clouds. We present Cosmic Background Imager (CBI) cm-wave data of two translucent clouds, {\zeta} Oph and LDN 1780 with the aim of characterising the anomalous emission in the translucent cloud environment. In {\zeta} Oph, the measured brightness at 31 GHz is 2.4{\sigma} higher than an extrapolation from 5 GHz measurements assuming a free-free spectrum on 8 arcmin scales. The SED of this cloud on angular scales of 1{\odot} is dominated by free-free emission in the cm-range. In LDN 1780 we detected a 3 {\sigma} excess in the SED on angular scales of 1{\odot} that can be fitted using a spinning dust model. In this cloud, there is a spatial correlation between the CBI data and IR images, which trace dust. The correlation is better with near-IR templates (IRAS 12 and 25 {\mu}m) than with IRAS 100 {\mu}m, which suggests a very small grain origin for the emission at 31 GHz. We calculated the 31 GHz emissivities in both clouds. They are similar and have intermediate values between that of cirrus clouds and dark clouds. Nevertheless, we found an indication of an inverse relationship between emissivity and column density, which further supports the VSGs origin for the cm-emission since the proportion of big relative to small grains is smaller in diffuse clouds.

Among herbaceous species of Hypericum with surficially glandular-punctate leaves and quadrate, narrowly winged stems, the five taxa of the “Hypericum denticulatum complex” of southeastern United States have in common petals that are strongly inequilateral, orange-yellow, ca. 1 cm long and 0.5 cm wide; stamens numerous (50–80); and styles comparatively long (2–4 mm). Three of the species are obligate wetland plants: H. denticulatum, H. harperi, and H. erythreae. The last-named, until now wrongly synonymized, is a species of the Atlantic Coastal Plain of southeastern Georgia and, historically, southern South Carolina. It resembles the mostly more northern H. denticulatum in having appressed or ascending leaves that are shorter than their internodes and in growing in boggy habitats, but is a taller plant that also differs by its notably sparse leaves that are distinctly reduced upward and on average proportionately narrower. The remaining two species are obligate upland plants: H. virgatum and H. ra...