The ATLAS-SPT radio survey of cluster galaxies

Galaxy clusters are the largest gravitationally bound objects in the Universe. The study of galaxy clusters can give insights into the large-scale structure of the Universe and provide constraints on the cosmological parameters that dictate the evolution of the Universe. Bent-tail radio sources are a class of Active Galactic Nuclei (AGN) where the jets or lobes have been distorted significantly due to the relative movement through a dense medium. This behaviour is expected to occur in galaxy clusters, especially those of high mass. I have planned and carried out the observations for the ATLAS-SPT survey, a radio continuum survey of ~86 deg2 using the Australia Telescope Compact Array at a central observing frequency of 2.1GHz over a bandwidth of 2GHz, with the telescope in an extended array configuration with a maximum baseline length of 6 km. The calibrated dataset was imaged, deconvolved using a multi-frequency deconvolution algorithm, and corrected for wide-bandwidth primary beam effects to produce total intensity and spectral variation images for each pointing. The limited u, v coverage of the survey caused several imaging challenges; the most significant being a poorly behaved synthesised beam response pattern and sidelobes from moderately bright outlier sources producing image artefacts. I devised an imaging pipeline which minimised the outlier source artefacts by employing a two-stage imaging process: 1) each pointing was imaged well beyond the primary beam with a coarse pixel resolution to find bright outlying sources; 2) outlying sources with a brightness expected to produce a synthesised beam pattern above the thermal noise of the pointing were modelled and subtracted from the pointing dataset. After subtracting the outlying sources, imaging could proceed as normal. Once each pointing was imaged, they were convolved with a Gaussian to produce a common angular resolution of 800 and linearly mosaicked to produce two images of the entire field: one total intensity mosaic and a spectral index mosaic. Due to limitations in the mosaicking software, 9 overlapping mosaic tiles were produced and subsequently combined with a custom imaging script. The final combined total intensity mosaic contains approximately 43 000 x 40 000 px and has a median rms noise level of approximately 180 μJy. I have produced a radio source catalogue containing positions and flux densities of 6067 sources. 722 of these sources have sufficient signal-to-noise ratios to provide a reliable spectral index measurement which is also included in the catalogue. I conducted a completeness simulation which indicates that the catalogue is 100% complete at the 1.3mJy beam−1 flux density level. This simulation was also used to estimate the flux density and positional accuracies. Due to noise fluctuations, flux densities of the faintest catalogued sources (~0.36mJy beam−1) are boosted by ~30%, and the boosting level falls below 5% for sources ≥$0.74mJy beam−1. The extracted positions have a median offset of ≪1" from their simulated input positions with a standard deviation of σ = 1.6" for the faintest sources, improving to σ = 0.5" for sources with flux densities ≥$1.3mJy beam−1. The catalogue was also matched and compared with the ATCA-XXL survey which covered the inner 25 deg2 of the field to a greater sensitivity. The matched sources are shown to be in excellent flux density and positional agreement. I constructed a Euclidean-normalised differential source count using the ATLAS-SPT catalogue, incorporating the necessary flux density corrections from the completeness simulation. The source counts agree well with others from the literature. The result confirms that the ATLAS-SPT survey is most sensitive to AGN and the steepening of the source counts clearly show the evolution of these sources. The source counts toward the catalogue sensitivity limit show the characteristic flattening, indicating the increased population of star-forming galaxies at those flux densities. I have identified 50 bent-tail radio galaxy candidates from the ATLAS-SPT total intensity mosaic by visual inspection and cross-matched these sources with the deep 3.6 μm Spitzer– South Pole Telescope Deep Field (SSDF) catalogue of the field. I then cross-matched the SSDF sources to both the Blanco Cosmology Survey (BCS) and Dark Energy Survey (DES) Science Verification catalogues and provide photometric redshift estimates for 17 bent-tail candidates. I then cross-matched these bent-tail candidates with redshifts to known cluster catalogues (546 in total). I found that only 4 are associated with known clusters. Recent models when applied to this dataset predict that ~7 bent-tail sources should be associated with high-mass (M ≥ 10 15M.) clusters such as those from the SPT SZ cluster catalogue. Instead I find only one. The lack of bent-tail sources within clusters may be explained by various effects such as projection, resolution, and AGN duty cycle. However, the lack of clusters found around bent-tail sources is more problematic and suggests that bent-tails may reside in cluster of lower mass than expected

The Spatial Correlation of Bent-Tail Galaxies and Galaxy Clusters

We have completed a deep radio continuum survey covering 86 square degrees of the Spitzer-South Pole Telescope deep field to test whether bent-tail galaxies are associated with galaxy clusters. We present a new catalogue of 22 bent-tail galaxies and a further 24 candidate bent-tail galaxies. Surprisingly, of the 8 bent-tail galaxies with photometric redshifts, only two are associated with known clusters. While the absence of bent-tail sources in known clusters may be explained by effects such as sensitivity, the absence of known clusters associated with most bent-tail galaxies casts doubt upon current models of bent-tail galaxies.Comment: Accepted by MNRA

LMC X-1: A New Spectral Analysis of the O-star in the binary and surrounding nebula

We provide new observations of the LMC X-1 O star and its extended nebula structure using spectroscopic data from VLT/UVES as well as H$\alpha$ imaging from the Wide Field Imager on the Max Planck Gesellschaft / European Southern Observatory 2.2m telescope and ATCA imaging of the 2.1 GHz radio continuum. This nebula is one of the few known to be energized by an X-ray binary. We use a new spectrum extraction technique that is superior to other methods to obtain both radial velocities and fluxes. This provides an updated spatial velocity of $\simeq 21.0~\pm~4.8$ km s$^{-1}$ for the O star. The slit encompasses both the photo-ionized and shock-ionized regions of the nebula. The imaging shows a clear arc-like structure reminiscent of a wind bow shock in between the ionization cone and shock-ionized nebula. The observed structure can be fit well by the parabolic shape of a wind bow shock. If an interpretation of a wind bow shock system is valid, we investigate the N159-O1 star cluster as a potential parent of the system, suggesting a progenitor mass of $\sim 60$ M$_{\odot}$ for the black hole. We further note that the radio emission could be non-thermal emission from the wind bow shock, or synchrotron emission associated with the jet inflated nebula. For both wind and jet-powered origins, this would represent one of the first radio detections of such a structure.Comment: 7 Figures, 4 Table

The ATLAS-SPT radio survey of cluster galaxies

Using a high-performance computing cluster to mosaic 4,787 pointings, we have imaged the 100 sq. deg. South Pole Telescope (SPT) deep-field at 2.1 GHz using the Australian Telescope Compact Array to an rms of 80 mJy and a resolution of 8". Our goal is to generate an independent sample of radio-selected galaxy clusters to study how the radio properties compare with cluster properties at other wavelengths, over a wide range of redshifts in order to construct a timeline of their evolution out to z ~ 1:3. A preliminary analysis of the source catalogue suggests there is no spatial correlation between the clusters identified in the SPT-SZ catalogue and our wide-angle tail galaxies

Mycobacterium ulcerans treatment - can antibiotic duration be reduced in selected patients?

Mycobacterium ulcerans (M. ulcerans) is a necrotizing skin infection endemic to the Bellarine Peninsula, Australia. Current treatment recommendations include 8 weeks of combination antibiotics, with adjuvant surgery if necessary. However, antibiotic toxicity often results in early treatment cessation and local experience suggests that shorter antibiotic courses may be effective with concurrent surgery. We report the outcomes of patients in the Barwon Health M. ulcerans cohort who received shorter courses of antibiotic therapy than 8 weeks

Quantifiable study of magnetic resonance super resolution reconstruction in Placenta Accreta Spectrum using Image Quality Metrics

Magnetic Resonance Images are increasingly being used for detection and diagnosis of Placental Complications1 . Here we apply this technology to reconstruction of placenta accreta spectrum. Super-Resolution Reconstruction (SRR) allows for a high-resolution 3D reconstruction from 2D MRI slices to allow for improved visibility of structures for future clinical use2 . The use of Image Quality metrics provides quantitative evaluation of the SRR images and allows comparisons to be drawn between the original 2D images and the SRR. These metrics are tested for statistical significance, providing an objective assessment of the SRR images

Mycobacterium ulcerans disease: experience with primary oral medical therapy in an Australian cohort

Mycobacterium ulcerans (MU) is responsible for disfiguring skin infections which are challenging to treat. The recommended treatment for MU has continued to evolve from surgery to remove all involved tissue, to the use of effective combination oral antibiotics with surgery as required. Our study describes the oral medical treatment utilised for consecutive cases of MU infection over a 15 month period at our institution, in Victoria, Australia. Managing patients primarily with oral antibiotics results in high cure rates and excellent cosmetic outcomes. The success with medical treatment reported in this study will aid those treating cases of MU infection, and will add to the growing body of knowledge about the relative roles of antibiotics and surgery for treating this infection

New insights into polymer mediated formation of anatase mesocrystals

The reaction between (NH4)2TiF6 and H3BO3 in the presence of varying quantities of PEG-6000 was used to form NH4TiOF3 mesocrystals (MCs). The amount of PEG-6000, employed as a template, is crucial to the formation of defect free, non-agglomerated NH4TiOF3 MCs; high concentrations lead to MC agglomeration, lower ones result in centralized defects. This polymer-mediated formation process may be understood using an analogy with known polymerization reactions. The oxofluorotitanate MCs readily undergo a thermal topotactic transformation to give anatase MCs with photocatalytic activity. The TiO2 MCs are porous, with highly orientated lamellar crystallites that form part of the larger mesocrystal structure

SROI in the art gallery: valuing social impact

This article considers a project that used the Social Return on Investment (SROI) methodology to describe and measure the social impact of Turner Contemporary art gallery in Margate, a coastal town in the South East of England. The article details the reasons why the methodology was chosen by the gallery, setting this in the context of the wider debate around evaluation and social impact reporting. A section of the research and analysis, which was carried out by COaST, a consultancy and research centre based within Canterbury Christ Church University, is described in detail, allowing the reader to understand the processes involved in this type of project and the kinds of outcomes that can be delivered using this method. Finally, an account is given of the impact the work had on the management of the gallery, and the ways in which the final report was used

Successful Outcomes with Oral Fluoroquinolones Combined with Rifampicin in the Treatment of Mycobacterium ulcerans: An Observational Cohort Study

Buruli ulcer is a necrotizing infection of skin and subcutaneous tissue caused by Mycobacterium ulcerans and is the third most common mycobacterial disease worldwide (after tuberculosis and leprosy). In recent years its treatment has radically changed, evolving from a predominantly surgically to a predominantly medically treated disease. The World Health Organization now recommends combined streptomycin and rifampicin antibiotic treatment as first-line therapy for Mycobacterium ulcerans infections. However, alternatives are needed where recommended antibiotics are not tolerated or accepted by patients, contraindicated, or not accessible nor affordable. This study describes the use of antibiotics, including oral fluoroquinolones, in the treatment of Mycobacterium ulcerans in south-eastern Australia. It demonstrates that antibiotics combined with surgery are highly effective in the treatment of Mycobacterium ulcerans. In addition, oral fluoroquinolone-containing antibiotic combinations are shown to be as effective and well tolerated as other recommended antibiotic combinations. Fluoroquinolone antibiotics therefore offer the potential to provide an alternative oral antibiotic to be combined with rifampicin for Mycobacterium ulcerans treatment, allowing more accessible and acceptable, less toxic, and less expensive treatment regimens to be available, especially in resource-limited settings where the disease burden is greatest