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Chung S.K.,University of Western Australia | Wen L.,University of Western Australia | Wen L.,International Center for Radio Astronomy Research | Blair D.,University of Western Australia | And 2 more authors.
Classical and Quantum Gravity | Year: 2010

We report a novel application of a graphics processing unit (GPU) for the purpose of accelerating the search pipelines for gravitational waves from coalescing binaries of compact objects. A speed-up of 16-fold in total has been achieved with an NVIDIA GeForce 8800 Ultra GPU card compared with one core of a 2.5 GHz Intel Q9300 central processing unit (CPU). We show that substantial improvements are possible and discuss the reduction in CPU count required for the detection of inspiral sources afforded by the use of GPUs. © 2010 IOP Publishing Ltd.

Wong O.I.,International Center for Radio Astronomy Research | Meurer G.R.,International Center for Radio Astronomy Research | Meurer G.R.,University of Western Australia | Zheng Z.,CAS National Astronomical Observatories | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We examine the HI-based star formation efficiency (SFEHI), the ratio of star formation rate to the atomic hydrogen (H I) mass, in the context of a constant stability star-forming disc model. Our observations of HI-selected galaxies show SFEHI to be fairly constant (log SFEHI = -9.65 yr-1 with a dispersion of 0.3 dex) across ~5 orders of magnitude in stellar masses. We present a model to account for this result, whose main principle is that the gas within galaxies forms a uniform stability disc and that stars form within the molecular gas in this disc. We test two versions of the model differing in the prescription that determines the molecular gas fraction, based on either the hydrostatic pressure or the stellar surface density of the disc. For high-mass galaxies such as the Milky Way, we find that either prescription predicts SFEHI similar to the observations. However, the hydrostatic pressure prescription is a more accurate SFEHI predictor for low-mass galaxies. Our model is the first model that links the uniform SFEHI observed in galaxies at low redshifts to star-forming discs with constant marginal stability. While the rotational amplitude Vmax is the primary driver of disc structure in our model, we find that the specific angular momentum of the galaxy may play a role in explaining a weak correlation between SFEHI and effective surface brightness of the disc. © 2016 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Dodson R.,International Center for Radio Astronomy Research | Moriarty C.D.,International Center for Radio Astronomy Research
Monthly Notices of the Royal Astronomical Society | Year: 2012

Methanol masers can provide valuable insight into the processes involved in high mass star formation; however, the local environment in which they form is still unclear. Four primary, yet conflicting, models have emerged to explain the commonly observed methanol maser structures at 6.67 GHz. These suggest that masers trace accretion discs, outflows, shock fronts or discs dominated by infall/outflows. One proposed means of testing these models is through mapping the local magnetic field structures around maser sources, which were predicted to lie parallel to shock and outflows and perpendicular to accretion discs. To follow up this suggestion, we have determined magnetic field directions from full polarization observations of 10 6.67-GHz sources. We find morphology that is parallel to the source structure, indicative of shocks or outflows, in five sources and perpendicular morphology indicative of discs in three sources. These results do not support any of the expected models and the diverse morphologies observed indicate that the masers could be emitting from different evolutionary stages or environments, or from a common local environment with complex associated magnetic fields. To resolve this conflict, we suggest a new approach that will search the simulations of massive star formation, which are just becoming available, for suitable sites for maser emission. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Macpherson D.,International Center for Radio Astronomy Research
Monthly Notices of the Royal Astronomical Society | Year: 2015

We investigate the prospects of detecting radio afterglows from long Gamma-Ray Bursts (GRBs) from Population III (Pop III) progenitors using the Square Kilometre Array (SKA) precursor instruments MWA (Murchison Widefield Array) and ASKAP (Australian SKA Pathfinder).We derive a realistic model of GRB afterglows that encompasses the widest range of plausible physical parameters and observation angles. We define the best case scenario of Pop III GRB energy and redshift distributions. Using probability distribution functions fitted to the observed microphysical parameters of long GRBs, we simulate a large number of Pop III GRB afterglows to find the global probability of detection. We find that ASKAP may be able to detect 35 per cent of Pop III GRB afterglows in the optimistic case, and 27 per cent in the pessimistic case. A negligible number will be detectable by MWA in either case. Detections per image for ASKAP, found by incorporating intrinsic rates with detectable time-scales, are as high as ~6000 and as low as ~11, which shows the optimistic case is unrealistic. We track how the afterglow flux density changes over various time intervals and find that, because of their very slow variability, the cadence for blind searches of these afterglows should be as long as possible. We also find Pop III GRBs at high redshift have radio afterglow light curves that are indistinguishable from those of regular long GRBs in the more local Universe. © 2015 The Authors.

Researchers in Australia have developed a new method of surveying the sky using radio telescopes that has allowed them to finally see what lies beyond the expanse of the Milky Way. In a study featured in the Astrophysical Journal, Prof. Lister Staveley-Smith and his colleagues at the International Center for Radio Astronomy Research (ICRAR) were able to take a peek behind the Milky Way galaxy using CSIRO's Parkes Radio Telescope that has been fitted with a new receiver. Scientists have long sought to find out what could be found in that area of space, particularly where a massive gravitational anomaly known as the Great Attractor that is located some 150 and 250 million light years away from the Milky Way. Previous theories have suggested that this region possibly contains a large collection of stars and galaxies, but these have yet to be confirmed. The presence of the bright and expansive disk of the Milky Way has prevented astronomers from studying the area using visible wavelengths. "The Milky Way is very beautiful of course and it's very interesting to study our own galaxy but it completely blocks out the view of the more distant galaxies behind it," Staveley-Smith said. While the researchers tried to use various techniques to see pass the Milky Way, they were only able to peek through thick foreground layer of stars and dust after using radio observations of the sky. Astronomers first became aware of the existence of the Great Attractor after conducting sky surveys in 1973 and in 1978. However, it wasn't until 1986 that they were able to provide estimates of where the gravitational anomaly could be. The Great Attractor is believed to be somewhere in the vicinity of the constellations Norma (The Carpenter's Square) and Triangulum Australe (The Southern Triangle). This area of space also includes the Norma Cluster (Abell 3627) and a dense portion of the Milk Way. Staveley-Smith and his team have been trying to find out more about the Great Attractor, which is said to have a gravitational force that is comparable to that of a million billion suns. The phenomenon continues to be one of the biggest mysteries in astronomy, but the recent success of the ICRAR researchers in seeing beyond the Milk Way in their survey could provide an important piece to finally solving this cosmic puzzle. Staveley-Smith said that they have yet to determine the potential cause of the acceleration of gravity in the Milky Way or where the phenomenon is coming from. What they do know, however, is that the region is home to a large number of galaxies known as superclusters, and that the entire Milky Way is traveling toward these clusters at a speed over two million kilometers per hour. The researchers were able to identify three dense galaxy concentrations as well as two new clusters, which could be contributing to the massive flow of galaxies toward that direction. Study co-author Renée Kraan-Korteweg said that a galaxy is typically made up of 100 billion stars. Discovering hundreds of additional galaxies behind the Milky Way means that there is a large amount of mass in that area of space that scientists did not know existed until now.

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