International Center for Radio Astronomy Research

Crawley, Australia

International Center for Radio Astronomy Research

Crawley, Australia

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Sweet S.M.,University of Queensland | Drinkwater M.J.,University of Queensland | Meurer G.,University of Western Australia | Meurer G.,International Center for Radio Astronomy Research | And 7 more authors.
Astrophysical Journal | Year: 2014

We present a recalibration of the luminosity-metallicity relation for gas-rich, star-forming dwarfs to magnitudes as faint as MR -13. We use the Dopita et al. metallicity calibrations to calibrate the relation for all the data in this analysis. In metallicity-luminosity space, we find two subpopulations within a sample of high-confidence Sloan Digital Sky Survey (SDSS) DR8 star-forming galaxies: 52% are metal-rich giants and 48% are metal-medium galaxies. Metal-rich dwarfs classified as tidal dwarf galaxy (TDG) candidates in the literature are typically of metallicity 12 + log(O/H) = 8.70 ± 0.05, while SDSS dwarfs fainter than MR = -16 have a mean metallicity of 12 + log(O/H) = 8.28 ± 0.10, regardless of their luminosity, indicating that there is an approximate floor to the metallicity of low-luminosity galaxies. Our hydrodynamical simulations predict that TDGs should have metallicities elevated above the normal luminosity-metallicity relation. Metallicity can therefore be a useful diagnostic for identifying TDG candidate populations in the absence of tidal tails. At magnitudes brighter than MR -16, our sample of 53 star-forming galaxies in 9 H I gas-rich groups is consistent with the normal relation defined by the SDSS sample. At fainter magnitudes, there is an increase in dispersion of the metallicity of our sample, suggestive of a wide range of H I content and environment. In our sample, we identify three (16% of dwarfs) strong TDG candidates (12 + log(O/H) > 8.6) and four (21%) very metal-poor dwarfs (12 + log(O/H) < 8.0), which are likely gas-rich dwarfs with recently ignited star formation. © 2014. The American Astronomical Society. All rights reserved..


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.


Sweet S.M.,Australian National University | Drinkwater M.J.,University of QueenslandQLD | Meurer G.,University of Western Australia | Meurer G.,International Center for Radio Astronomy Research | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We present DEIMOS multi-object spectroscopy (MOS) of 22 star-forming dwarf galaxies located in four gas-rich groups, including six newly discovered dwarfs. Two of the galaxies are strong tidal dwarf galaxy (TDG) candidates based on our luminosity-metallicity relation definition. We model the rotation curves of these galaxies. Our sample shows low mass-tolight ratios (M/L = 0.73 ± 0.39M⊙/L⊙) as expected for young, star-forming dwarfs. One of the galaxies in our sample has an apparently strongly falling rotation curve, reaching zero rotational velocity outside the turnover radius of rturn = 1.2re. This may be (1) a polar ring galaxy, with a tilted bar within a face-on disc; (2) a kinematic warp. These scenarios are indistinguishable with our current data due to limitations of slit alignment inherent to MOSmode observations. We consider whether TDGs can be detected based on their tidal radius, beyond which tidal stripping removes kinematic tracers such as Ha emission. When the tidal radius is less than about twice the turnover radius, the expected falling rotation curve cannot be reliably measured. This is problematic for as much as half of our sample, and indeed more generally, galaxies in groups like these. Further to this, the Ha light that remains must be sufficiently bright to be detected; this is only the case for three (14 per cent) galaxies in our sample. We conclude that the falling rotation curves expected of TDGs are intrinsically difficult to detect. © 2015 The Authors.


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.


Trayford J.W.,Durham University | Theuns T.,Durham University | Bower R.G.,Durham University | Crain R.A.,Liverpool John Moores University | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We examine the evolution of intrinsic u-r colours of galaxies in the EAGLE cosmological hydrodynamical simulations, which has been shown to reproduce the observed redshift z = 0.1 colour-magnitude distribution well, with a focus on z < 2. The median u-r of star-forming ('blue cloud') galaxies reddens by 1 mag from z = 2 to 0 at fixed stellar mass, as their specific star formation rates decrease with time. A red sequence starts to build-up around z = 1, due to the quenching of low-mass satellite galaxies at the faint end, and due to the quenching of more massive central galaxies by their active galactic nuclei (AGN) at the bright end. This leaves a dearth of intermediate-mass red sequence galaxies at z = 1, which is mostly filled in by z = 0. We quantify the time-scales of colour transition finding that most galaxies spend less than 2 Gyr in the 'green valley'. We find the time-scale of transition to be independent of quenching mechanism, i.e. whether a galaxy is a satellite or hosting an AGN. On examining the trajectories of galaxies in a colour-stellar mass diagram, we identify three characteristic tracks that galaxies follow (quiescently star-forming, quenching and rejuvenating galaxies) and quantify the fraction of galaxies that follow each track. © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


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.


Morgan J.S.,National institute for astrophysics | Morgan J.S.,Max Planck Institute for Radio Astronomy | Morgan J.S.,Curtin University Australia | Morgan J.S.,International Center for Radio Astronomy Research | And 7 more authors.
Astronomy and Astrophysics | Year: 2011

For Very Long Baseline Interferometry (VLBI), the fringe spacing is extremely narrow compared to the field of view imposed by the primary beam of each element. This means that an extremely large number of resolution units can potentially be imaged from a single observation. We implement and test a technique for efficiently and accurately imaging large VLBI datasets. The DiFX software correlator is used to generate a dataset with extremely high time and frequency resolution. This large dataset is then transformed and averaged multiple times to generate many smaller datasets, each with a phase centre located at a different area of interest. Results of an 8.4GHz four-station VLBI observation of a field containing multiple sources are presented. Observations of the calibrator 3C345 were used for preliminary tests of accuracy of the shifting algorithm. A high level of accuracy was achieved, making the method suitable even for the most demanding astrometric VLBI observations. One target source (1320+299A) was detected and was used as a phase-reference calibrator in searching for further detections. An image containing 13 billion pixels was constructed by independently imaging 782 visibility datasets covering the entire primary beam of the array. Current implementations of this algorithm and possible future developments in VLBI data analysis are discussed. © 2011 ESO.


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.


News Article | October 21, 2016
Site: www.techtimes.com

A grand hydrogen map of the Milky Way has been prepared by scientists for the first time, revealing new information regarding the spaces between stars. The superior map HI4PI was compiled after taking vast data from two huge radio telescopes: the Max Planck radio telescope in Germany and CSIRO radio telescope in Australia. The HI4PI survey mapped neutral atomic hydrogen, considering its abundance in space and status as the main component of stars and galaxies. The meticulous study comes after millions of personal observations and data points that numbered more than 10 billion. Published in Astronomy & Astrophysics, the new mapping scores over a previous study, which was named the Leiden-Argentine-Bonn (LAB) survey in terms of sensitivity and angular resolution. Reflecting on the merits of the new map, University of Bonn astronomer Jürgen Kerp called it a big leap over the earlier study, which was hamstrung by the difficult sampling of the sky. According to him, in HI4PI data, pilot studies were showing a wealth of structures unseen before. In the new map, even tiny clouds are visible. That is important because they are vital as having been instrumental in hastening the formation of stars in the Milky Way. Thanks to more than a million individual observations, the new outcome is telling the tale with all fine details of the structures between stars, according to the German and Australian scientists. The data gathered by the big radio telescopes reflect the cumulative hydrogen content and explain the locations of so many dwarf galaxies. "We've been able to produce a whole-sky image that in many ways are greater than the sum of its parts," Lister Staveley-Smith of the International Center for Radio Astronomy Research (ICRAR) said. Star formation in the Milky Way for billions of years has been abetted by gas clouds. From the map, convincing answers on questions related to the Milky Way, and galaxies in the neighborhood, can be obtained. According to Staveley-Smith, mysteries such as the source of gas for the Milky Way for sustained star formation and the position of dwarf galaxies have been answered by the new study, and it certainly has more excitement in store. The project, which used 10 billion individual data points, revealed that the Milky Way as a galactic home contains 400 billion stars. The distance of the solar system from the Galactic Center is an average 27,000 light years. In short, the HI4PI map marks the great strides made in astronomy after the advent of new telescopes and use of latest scientific techniques. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.


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.

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