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  • richardmitnick 2:11 pm on March 28, 2017 Permalink | Reply
    Tags: , , CAASTRO, , , ,   

    From ICRAR: “Astronomers probe swirling particles in halo of starburst galaxy’ 

    ICRAR Logo
    International Centre for Radio Astronomy Research

    March 28, 2017

    1
    NGC253 starburst galaxy in optical (green; SINGG Survey) and radio (red; GLEAM) wavelengths. The H-alpha line emission, which indicates regions of active star formation, is highlighted in blue (SINGG Survey; Meurer+2006). Credits: A.D. Kapinska, G. Meurer. ICRAR/UWA/CAASTRO.

    Astronomers have used a radio telescope in outback Western Australia to see the halo of a nearby starburst galaxy in unprecedented detail.

    A starburst galaxy is a galaxy experiencing a period of intense star formation and this one, known as NGC 253 or the Sculptor Galaxy, is approximately 11.5 million light-years from Earth.

    “The Sculptor Galaxy is currently forming stars at a rate of five solar masses each year, which is a many times faster than our own Milky Way,” said lead researcher Dr Anna Kapinska, from The University of Western Australia and the International Centre for Radio Astronomy Research (ICRAR) in Perth.

    The Sculptor Galaxy has an enormous halo of gas, dust and stars, which had not been observed before at frequencies below 300 MHz. The halo originates from galactic “fountains” caused by star formation in the disk and a super-wind coming from the galaxy’s core.

    The study used data from the ‘GaLactic and Extragalactic All-sky MWA’, or ‘GLEAM’ survey, which was observed by the Murchison Widefield Array (MWA) radio telescope located in remote Western Australia.

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    Murchison Widefield Array (MWA) radio telescope

    “With the GLEAM survey we were able, for the first time, to see this galaxy in its full glory with unprecedented sensitivity at low radio frequencies,” said Dr Kapinska.

    “We could see radio emission from electrons accelerated by supernova explosions spiralling in magnetic fields, and absorption by dense electron-ion plasma clouds —it’s absolutely fascinating.”

    The MWA is a precursor to the Square Kilometre Array (SKA) radio telescope, part of which will be built in Western Australia in the next decade.

    Co-author Professor Lister Staveley-Smith, from ICRAR and the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), said the SKA will be the largest radio telescope in the world and will be capable of discovering many new star-forming galaxies when it comes online.

    “But before we’re ready to conduct a large-scale survey of star-forming and starburst galaxies with the SKA we need to know as much as possible about these galaxies and what triggers their extreme rate of star formation,” he said.

    PUBLICATION DETAILS

    Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies, published in the Astrophysical Journal on March 28th, 2017.

    See the full article here .

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    ICRAR is an equal joint venture between Curtin University and The University of Western Australia with funding support from the State Government of Western Australia. The Centre’s headquarters are located at UWA, with research nodes at both UWA and the Curtin Institute for Radio Astronomy (CIRA).
    ICRAR has strong support from the government of Australia and is working closely with industry and the astronomy community, including CSIRO and the Australian Telescope National Facility, iVEC, and the international SKA Project Office (SPO), based in the UK.

    ICRAR is:

    Playing a key role in the international Square Kilometre Array (SKA) project, the world’s biggest ground-based telescope array.

    SKA Square Kilometer Array
    Attracting some of the world’s leading researchers in radio astronomy, who will also contribute to national and international scientific and technical programs for SKA and ASKAP.
    Creating a collaborative environment for scientists and engineers to engage and work with industry to produce studies, prototypes and systems linked to the overall scientific success of the SKA, MWA and ASKAP.

    SKA Murchison Widefield Array
    A Small part of the Murchison Widefield Array

    Enhancing Australia’s position in the international SKA program by contributing to the development process for the SKA in scientific, technological and operational areas.
    Promoting scientific, technical, commercial and educational opportunities through public outreach, educational material, training students and collaborative developments with national and international educational organisations.
    Establishing and maintaining a pool of emerging and top-level scientists and technologists in the disciplines related to radio astronomy through appointments and training.
    Making world-class contributions to SKA science, with emphasis on the signature science themes associated with surveys for neutral hydrogen and variable (transient) radio sources.
    Making world-class contributions to SKA capability with respect to developments in the areas of Data Intensive Science and support for the Murchison Radio-astronomy Observatory.

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  • richardmitnick 11:22 am on September 29, 2016 Permalink | Reply
    Tags: Analysing galaxy evolution in EAGLE, Angular momentum is a fundamental property of galaxies, , , CAASTRO   

    From CAASTRO: “EAGLE simulation shows gain & loss of galaxies’ angular momentum” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    29 September 2016
    No writer credit

    Angular momentum is a fundamental property of galaxies, together with mass and energy. It is crucial to many scaling relations, for example the relation between a galaxy’s luminosity and its rotational velocity and size. Galaxy formation theory postulates that the amount of angular momentum in spiral galaxies can be obtained by assuming that they formed in dark matter halos through conservation of angular momentum. Elliptical galaxies though, which have much lower spins, need to lose more than 90% of the angular momentum they were formed with. Galaxy mergers are the main scenario invoked to explain such a major loss.

    1

    In a new publication, CAASTRO member Dr Claudia Lagos (ICRAR-UWA) and colleagues analysed the evolution of the angular momentum of galaxies in the EAGLE hydrodynamical simulations. EAGLE is a state-of-the-art simulation that has a unique compromise between the resolution required to study the structural properties of galaxies (spatial resolution of 700 pc) and the simulated cosmological volume (100 Mpc box side length). This allows for the study of about 13,000 galaxies in the simulation-equivalent of the local Universe. EAGLE is unique in its accurate reconstruction of galaxy properties across multiple research studies, predicting galaxies of roughly the right sizes, morphologies, colours, gas contents and star formation throughout cosmic time.

    This new study has found a correlation between the galaxies’ specific angular momentum (i.e. angular momentum as function of mass) and their stellar mass – in excellent agreement with observations and with the positions of galaxies as they correlate with gas content.

    Analysing galaxy evolution in EAGLE paints a picture that is more complex than what theory predicted: galaxies that have high specific angular momentum now formed most of their stars during the second half of the age of the Universe, from gas that was falling into their halos with high specific angular momentum. In contrast, galaxies that have low specific angular momentum now formed most of their stars during the first half of the age of the Universe, from material that had much lower specific angular momentum compared to the infalling gas later. The researchers conclude that the simple picture of two alternative scenarios – conservation of specific angular momentum or mergers that spin-down galaxies – does not capture what EAGLE has revealed to happen. How quickly a galaxy spins appears to depend on the individual star formation history with a contribution from the merger history.

    Publication details:
    Claudia Lagos et al. in the Monthly Notices of the Royal Astronomical Society (2016): Angular momentum evolution of galaxies in EAGLE

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO is a collaboration of The University of Sydney, The Australian National University, The University of Melbourne, Swinburne University of Technology, The University of Queensland, The University of Western Australia and Curtin University, the latter two participating together as the International Centre for Radio Astronomy Research (ICRAR). CAASTRO is funded under the Australian Research Council (ARC) Centre of Excellence program, with additional funding from the seven participating universities and from the NSW State Government’s Science Leveraging Fund.

     
  • richardmitnick 4:47 pm on September 15, 2016 Permalink | Reply
    Tags: Astronomers shed light on different galaxy types, , , CAASTRO   

    From CAASTRO: “Astronomers shed light on different galaxy types” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    14 September 2016
    Contacts:

    Dr Luca Cortese (University of Western Australia, ICRAR)
    Ph: +61 481 358 114 E: Luca.Cortese@icrar.org

    Prof Warrick Couch (Australian Astronomical Observatory, CAASTRO)
    Ph: + 61 2 9372 4811 E: Warrick.Couch@aao.gov.au

    Dr Wiebke Ebeling (CAASTRO, media contact)
    Ph: + 61 8 9266 9174 E: Wiebke.Ebeling@curtin.edu.au

    In research published today [MNRAS], Australian scientists have taken a critical step towards understanding why different types of galaxies exist throughout the Universe.

    The research, made possible by cutting-edge instrumentation, means that astronomers can now classify galaxies according to their physical properties rather than human interpretation of a galaxy’s appearance.

    For the past 100 years, telescopes have been capable of observing galaxies beyond our own galaxy, the Milky Way.

    Only a few were visible to begin with but as telescopes became more powerful, more galaxies were discovered, making it crucial for astronomers to come up with a way to consistently group different types of galaxies together.

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    In 1926, the famous American astronomer Edwin Hubble refined a system that classified galaxies into categories of spiral, elliptical, lenticular or irregular shape. This system, known as the Hubble sequence, is the most common way of classifying galaxies to this day.

    Despite its success, the criteria on which the Hubble scheme is based are subjective, and only indirectly related to the physical properties of galaxies. This has significantly hampered attempts to identify the evolutionary pathways followed by different types of galaxies as they slowly change over billions of years.

    Dr Luca Cortese, from The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), said the world’s premier astronomical facilities are now producing surveys consisting of hundreds of thousands of galaxies rather than the dozens that Hubble and his contemporaries were working with.

    “We really need a way to classify galaxies consistently using instruments that measure physical properties rather than a time consuming and subjective technique involving human interpretation,” he said.

    In a study led by Dr Cortese, a team of astronomers has used a technique known as Integral Field Spectroscopy to quantify how gas and stars move within galaxies and reinterpret the Hubble sequence as a physically based two-dimensional classification system.

    “Thanks to the development of new technologies, we can map in great detail the distribution and velocity of different components of galaxies. Then, using this information we’re able to determine the overall angular momentum of a galaxy, which is the key physical quantity affecting how the galaxy will evolve over billions of years.

    Remarkably, the galaxy types described by the Hubble scheme appear to be determined by two primary properties of galaxies–mass and angular momentum. This provides us with a physical interpretation for the well known Hubble sequence whilst removing the subjectiveness and bias of a visual classification based on human perception rather than actual measurement.”

    The new study involved 488 galaxies observed by the 3.9m Anglo Australian Telescope in New South Wales and an instrument attached to the telescope called the Sydney-AAO Multi-object Integral-field spectrograph or ‘SAMI’.

    AAO Anglo Australian Telescope Exterior near Siding Spring, New South Wales, AustraliaAAO Anglo Australian Telescope Interior
    AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia

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    SAMI

    The SAMI project, led by the University of Sydney and CAASTRO, aims to create one of the first large-scale resolved survey of galaxies, measuring the velocity and distribution of gas and stars of different ages in thousands of systems.

    “Australia has a lot of expertise with this type of astronomy and is really at the forefront of what’s being done,” said Professor Warrick Couch, Director of the Australian Astronomical Observatory and CAASTRO Partner Investigator.

    “For the SAMI instrument we succeeded in putting 61 optical fibres within a distance that’s less than half the width of a human hair.

    “That’s no small feat, it’s making this type of work possible and attracting interest from astronomers and observatories from around the world.”

    Future upgrades of the instrument are planned that will allow astronomers to obtain even sharper maps of galaxies and further their understanding of the physical processes shaping the Hubble sequence.

    “As we get better at doing this and the instruments we’re using are upgraded, we should be able to look for the physical triggers that cause one type of galaxy to evolve into another — that’s really exciting stuff,” Dr Cortese said.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO is a collaboration of The University of Sydney, The Australian National University, The University of Melbourne, Swinburne University of Technology, The University of Queensland, The University of Western Australia and Curtin University, the latter two participating together as the International Centre for Radio Astronomy Research (ICRAR). CAASTRO is funded under the Australian Research Council (ARC) Centre of Excellence program, with additional funding from the seven participating universities and from the NSW State Government’s Science Leveraging Fund.

     
  • richardmitnick 9:23 pm on August 16, 2016 Permalink | Reply
    Tags: , , CAASTRO, Star formation in galaxies   

    From CAASTRO: “Constant disk stability key to galactic star forming efficiency” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    17 August 2016
    No writer credit found

    Star formation in galaxies is a local process whereby stars form out of molecular Hydrogen (H2). Detailed multiwavelength studies of the gas and stellar components of nearby galaxies have found the H2 star formation efficiency (SFEh2) – the ratio of star formation rate to the H2 mass – to be approximately constant. Similarly, the atomic Hydrogen (HI) star formation efficiency (SFEhi) has also been observed to be uniform across 5 orders of magnitude in galaxy stellar masses. Since the fraction of HI and H2 is known to vary within a galaxy, as well as between galaxies, it is unclear what is driving the observed uniformity in SFEhi.

    1

    A new model, by CAASTRO Affiliate Dr Ivy Wong (ICRAR-UWA) and colleagues, is the first to link the uniform SFEhi observed in low-redshift galaxies to star-forming disks with constant marginal stability. In their simple model, disk stability is derived from a two-fluid approach: one fluid representing the gas component and the other the stellar component. The researchers tested two versions of their model with differing prescriptions for determining the molecular gas fraction, based on either the hydrostatic pressure or the stellar surface density of the modelled disk. For high-mass galaxies such as the Milky Way, they found that both prescriptions were able to reproduce the observed SFEhi. However, the hydrostatic prescription was the only prescription that was able to reproduce the observed SFEhi for both low- and high-mass galaxies. The primary driver of the disk structure in the model is the amplitude of the rotational velocity, Vmax, while the specific angular momentum of the galaxy may play a role in explaining the weak correlation between SFEhi and the effective surface brightness of the disk. The team was also able to reproduce the observed star formation properties of a proto-Milky Way at higher redshifts when the Universe was at its peak star formation period.

    The success of their model at reproducing the observed star formation properties in galaxies at low and high redshifts suggests that star formation in galaxies is largely governed by the formation and stabilisation of their disks.

    Publication details:
    Ivy Wong et al. in The Monthly Notices of the Royal Astronomical Society (2016): Characterising uniform star formation efficiencies with marginally-stable galactic disks

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

    PARTNER LINKS

    The University of Sydney
    The University of Western Australia
    The University of Melbourne
    Swinburne University of Technology
    The Australian National University
    Curtin University
    University of Queensland

     
  • richardmitnick 11:37 am on July 28, 2016 Permalink | Reply
    Tags: , , BoRG Survey, CAASTRO, Epoch of Reionisation   

    From CAASTRO: “The BoRG survey boosts numbers of earliest galaxies ever known” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    28 July 2016
    No writer credit found

    Between 100 million to one billion years after the Big Bang, the Universe went through a transition, where neutral hydrogen was ionised, transforming the intergalactic medium from opaque to transparent. This “Epoch of Reionisation” is receiving intense research focus, as there are still many open questions about this period. While future telescopes like the Square Kilometre Array (SKA) will be able to look at the neutral hydrogen, observing the stars and galaxies that were the sources of reionisation is still difficult.

    SKA Square Kilometer Array

    One possibility of investigating the formation and evolution of galaxies in the early Universe, along with the progression of reionisation, is to observe the ultraviolet light emitted by these high-redshift sources (stretched to be detected at infrared wavelengths from Earth) with space telescopes, located above the Earth’s atmosphere. Deep legacy surveys with the Hubble Space Telescope (HST) have produced a growing sample of galaxies during this period.

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    At the highest redshifts, the number of galaxy candidates is still small, with only a handful detected in HST imaging. To increase the sample, CAASTRO PhD student Stephanie Bernard (University of Melbourne), along with international collaborators, used HST/Wide Field Camera 3 (WFC3) imaging from the Brightest of Reionising Galaxies (BoRG) survey to search for the brightest galaxies only 500 million years after the Big Bang. The team found six interesting candidates in archival data. They conclude that half of the sample are strong candidates to be some of the highest-redshift galaxies so far discovered, while the other half likely to be lower-redshift sources.

    The researchers also calculated the “number density”, that is, the number of high-redshift galaxies in a given volume. They then determined the “luminosity function” or the number of galaxies at a particular brightness. Interestingly, when compared to previous calculations from surveys like the Cosmic Assembly Near-infrared Deep Intergalactic Legacy Survey (CANDELS), which also used WFC3 imaging, Bernard and her collaborators found almost ten times as many bright galaxies than expected. They also noted that three candidates in their sample are located in the same WFC3 pointing, which is an indication of significant clustering, as expected for very bright galaxies at high redshift. Ongoing follow-up observations by the team will shed more light on the nature of these candidate galaxies.

    Publication details:
    Bernard et al. in The Astrophysical Journal (2016): Galaxy candidates at z ~ 10 in archival data from the Brightest of Reionizing Galaxies (BoRG[z8]) survey

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

    PARTNER LINKS

    The University of Sydney
    The University of Western Australia
    The University of Melbourne
    Swinburne University of Technology
    The Australian National University
    Curtin University
    University of Queensland

     
  • richardmitnick 1:33 pm on April 26, 2016 Permalink | Reply
    Tags: , , CAASTRO, Intensity mapping   

    From CAASTRO: “Statistical tool beats radio telescopes in measuring distant gas” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    26 April 2016

    Intensity mapping is a novel technique that uses the Hydrogen emission at radio wavelengths of galaxies as a proxy for galaxy distribution on large scales. The statistical properties of this distribution help us understand the cosmological principles of our Universe. Hydrogen gas is the most abundant element in the Universe, and it is the main ingredient to fuel star-formation processes in galaxies and is thus driving galaxy evolution. The individual detection of cold Hydrogen gas in distant galaxies is not yet feasible with radio telescopes. However, using intensity mapping, we observe the combined – or binned – emission of many galaxies through low-resolution maps and are able to observe the Cosmic Web over very large distance ranges.

    The galaxy distribution is quantified by measuring the cosmological power spectrum. These power spectra contain information on the clustering strength of galaxies as a function of distance or scale. In recent analysis, the intensity mapping data was jointly analysed with optical data of the same regions to measure the cross-power spectrum, to eliminate foregrounds and instrumental noise contaminations in the maps.

    1

    As part of the CAASTRO intensity mapping project, CAASTRO post-doctoral fellow Dr Laura Wolz and colleagues at the University of Melbourne have theoretically investigated the signature of the cross-power spectrum of intensity maps with optical galaxy data. They modelled the intensity mapping signal using numerical simulations of the evolution of galaxies with cosmic time. In addition, they synthesised a mock galaxy catalogue of optical telescope observations based on the same simulation. In their study, the researchers show that the cross-power spectrum of intensity maps and optical galaxies has a different shape depending on how the optical galaxies were selected: blue galaxies, which are highly star-forming, show a much higher clustering signal on small scales than red galaxies, which are relatively passive. This proves that these signals can be linked back to the Hydrogen content of the optical galaxies as it correlates with the galaxy colour: blue galaxies are rich in cold gas while red galaxies are relatively gas poor. Intensity mapping in combination with optical galaxy measurements may therefore indirectly detect the Hydrogen gas content of the optical galaxies that were selected according to their colours. This theoretical study is the first proof of concept of this new Hydrogen detection technique, and the approach opens up new possibilities in understanding the gas content, and thus the star-formation activity, of very distant galaxies which are inaccessible to direct observations with our current generation of radio telescopes.

    Publication details:
    Laura Wolz, Chiara Tonini, Chris Blake & Stuart Wyithe in the Monthly Notices of the Royal Astronomical Society (2016): “Intensity Mapping Cross-Correlations: Connecting the Largest Scales to Galaxy Evolution

    [Both the Greenbank Telescope and Parkes Observatory were involved in this work.]

    Green Bank Radio Telescope, West Virginia, USA
    Green Bank Radio Telescope, West Virginia, USA

    CSIRO/Parkes Observatory
    CSIRO/Parkes Observatory

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

    PARTNER LINKS

    The University of Sydney
    The University of Western Australia
    The University of Melbourne
    Swinburne University of Technology
    The Australian National University
    Curtin University
    University of Queensland

     
  • richardmitnick 1:31 pm on April 20, 2016 Permalink | Reply
    Tags: , , CAASTRO, Could Fast Radio Bursts be of cosmological origin?,   

    From CAASTRO: “Could Fast Radio Bursts be of cosmological origin?” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    High time resolution radio surveys over the last decade have discovered a population of millisecond-duration transient bursts called Fast Radio Bursts (FRBs) of unknown. Only 18 of these bursts have been detected to date, and their origin – whether extragalactic or at even cosmological distances – is still uncertain.

    CAASTRO PhD student Manisha Caleb (ANU and Swinburne University of Technology) and colleagues have now scrutinised the FRB properties: energy distribution, spatial density as a function of redshift and properties of the Interstellar and Intergalactic Media. The researchers ran simulations to test whether a cosmological population is a feasible scenario and to compare their simulations to data from the High Time Resolution Universe survey that used the Effelsberg radio telescope in Germany and the 64-m Parkes radio telescope in Australia.

    MPIFR/Effelsberg Radio Telescope
    MPIFR/Effelsberg Radio Telescope

    CSIRO/Parkes Observatory
    CSIRO/Parkes Observatory

    Their Monte Carlo simulations were based on two scenarios for the co-moving numbers of FRBs: a constant co-moving density model and a model in which the number of FRBs is proportional to the known cosmic star formation history (SFH). The most interesting property of the simulated events is their distribution of detections above some fluence (so-called logN-logF curves): if the sources have an even approximately typical luminosity (i.e. are standard candle-like), then the slope of this relation is a probe of their spatial distribution. For standard candles in the standard model of cosmology – LCDM – the slope varies smoothly from -3/2 for the nearby universe, gradually becoming flatter as further distances are probed. To illustrate, at a redshift of z ~0.7, which is typical of FRBs found to date, standard candles yield a relation with a slope of ~ -1. The observed slope of the logN-logF of the 9 FRBs analysed in this study is -0.9 +/- 0.3. The team’s simulations were able, in both scenarios for the number density of the sources with redshift, to match this slope well, yielding -0.8 +/- 0.3 for the cosmic SFH and -0.7 +/- 0.2 for the constant density case. They concluded that the properties of the observed FRBs are generally consistent with arising from sources at cosmological distances.

    The researchers also simulated FRB rates at the upgraded Molonglo telescope, UTMOST, and at Parkes for the Multibeam and the planned Phased Array Feed (PAF) receivers.

    Molonglo Observatory Synthesis Telescope (MOST)
    Molonglo Observatory Synthesis Telescope (MOST)

    Parkes Phased Array Feed
    Parkes Phased Array Feed

    They applied conservative assumptions about the spectral index of FRBs and the sensitivity of the instruments. According to those simulations, UTMOST has the capability, at full design sensitivity, to dominate the FRB detection rate. Uncertainty in the final PAF design sensitivity make predictions difficult for Parkes but its wide sky coverage has the potential to increase the FRB discovery rate close to the fluence limit. The fully sensitive UTMOST will dominate the event detection rate at all fluences.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

    PARTNER LINKS

    The University of Sydney
    The University of Western Australia
    The University of Melbourne
    Swinburne University of Technology
    The Australian National University
    Curtin University
    University of Queensland

     
  • richardmitnick 10:24 am on April 7, 2016 Permalink | Reply
    Tags: , , CAASTRO, Zone of Avoidance   

    From CAASTRO: “Observing gas, mass and motions in the ‘Zone of Avoidance’ “ 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    7 April 2016

    We are not living in a fixed rest frame on Earth: the Earth is orbiting around the Sun, the Sun is moving around the centre of our galaxy, and the galaxy itself is moving towards the nearest mass over-density around us, which is the nearest galaxy cluster in Virgo.

    Milky Way's Spiral Arms NASAJPL Caltech ESO R. Hurt
    Milky Way NASA/JPL-Caltech ESO R. Hurt

    Similar motions arise from even larger scales and larger mass densities, such as the gravitational anomaly “Great Attractor”.

    Great Attractor galaxies
    Great Attractor galaxies

    To get a complete overview of these motions, we need a whole-sky map of the galaxies, together with these gravitationally induced motions.

    A major stumbling block in these efforts is our own galaxy, which blocks the sky behind it from our view. Many of the large-scale structures are hidden behind the dust and stellar density of our Milky Way, notably the Great Attractor, Perseus-Pisces Supercluster, Puppis Cluster and the Local Void. This results in the so-called “Zone of Avoidance” (ZoA).

    Zone of Avoidance. Spitzer.  GLIMPSE NASA JPL-Caltech R. Hurt SSC
    Zone of Avoidance. Spitzer. GLIMPSE NASA JPL-Caltech R. Hurt SSC

    Contrarily to optical light though, radio waves travel unhindered through the galaxy. Researchers are therefore using the Parkes radio telescope to measure the gas in galaxies hidden behind the Milky Way.

    CSIRO/Parkes Observatory
    CSIRO/Parkes Observatory

    Combining these observations with near infrared (NIR) imaging allows measuring the distance and gravitationally induced peculiar velocity via a distance indicator called the Tully-Fisher (TF) relation.

    1

    CAASTRO PhD student Khaled Said, who is jointly supervised by researchers at the Astrophysics, Cosmology and Gravity Centre at the University of Cape Town, South Africa, and CAASTRO Deputy Director Prof Lister Staveley-Smith (ICRAR-UWA), recently published his analysis of 290 new galaxy observations with the Parkes Multibeam Receiver. The team also used 104 additional galaxies from the existing HIZoA survey. The final sample contained 342 inclined spiral galaxies in the southern ZoA with adequate signal-to-noise and HI profiles suitable for their TF analysis.

    The aim of this analysis was the development of a systematic processing pipeline for HI line spectra for future applications of the TF relation in the ZoA. Their current sample, in conjunction with their previously published newly calibrated TF relation and current NIR data, will be the first accurate determination of flow fields in the southern ZoA. Their results will be an important contribution to the forthcoming WALLABY survey (Widefield ASKAP L-band Legacy All-sky Blind surveY) and its northern hemisphere counterpart, the Westerbork Northern Sky HI Survey (WNSHS).

    Publication details:
    Khaled Said et al. in MNRAS (2016): “NIR Tully-Fisher in the Zone of Avoidance. – II. 21 cm HI-line spectra of southern ZOA galaxies

    Science team:
    Khaled Said1,2,3⋆, Renée C. Kraan-Korteweg1, Lister Staveley-Smith2,3, Wendy L. Williams1,4,5, T. H. Jarrett1, and Christopher M. Springob2,3

    Affiliations:
    1 Astrophysics, Cosmology and Gravity Centre (ACGC), Astronomy Department, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa
    2 International Centre for Radio Astronomy Research (ICRAR), M468, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
    3 ARC Centre of Excellence for All-sky Astrophysics (CAASTRO)
    4 Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands
    5 Netherlands Institute for Radio Astronomy (ASTRON), PO Box 2, NL-7990 AA Dwingeloo, the Netherlands

    See the full article here .

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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

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  • richardmitnick 12:53 am on February 8, 2016 Permalink | Reply
    Tags: , , CAASTRO, Ultracool dwarfs   

    From CAASTRO: “Radio-loud ultracool dwarfs allow analysis of magnetic fields” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    8 February 2016
    No writer credit

    The group of lowest mass stars and brown dwarfs are collectively called ultracool dwarfs. A number of these objects are sources of both burst and quiescent radio emission. The radio bursts are sometimes found to occur periodically on the timescale of the rotation of the ultracool dwarf or as isolated events. They are highly circularly polarised and occur over a timescale of a few minutes. Alternatively, the quiescent emission is observed to have very little variability and low circular polarisation. Both radio emission components are thought to be the result of magnetic processes and imply that ultracool dwarfs are able to generate and sustain strong magnetic fields. This is unexpected though, given their non-solar-like interior and the observed decline in the strength of magnetic activity tracers at other wavelengths.

    Brown dwarf
    Artist’s concept of a T-type brown dwarf

    Radio surveys of ultracool dwarfs have found that about 10% of these systems are radio luminous, with 21 currently known to have radio emission. Correlations between the presence of radio emission and other dwarf properties such as rotation are not well established. Furthermore, little is known about the magnetic environment responsible for the radio emission observed in ultracool dwarfs. To address these issues, CAASTRO members Dr Christene Lynch and Dr Tara Murphy (University of Sydney), together with colleagues from Australia and overseas, carried out a survey of 15 ultracool dwarfs located in the Southern hemisphere using the Australia Telescope Compact Array [ATCA].

    CSIRO Australia Compact Array
    CSIRO ATCA

    ATCA is able to simultaneously observe over a wide range of frequencies, providing detailed information on the time-frequency structure of radio bursts and quiescent emission. Such a characterisation is required if we want to constrain the magnetic properties of ultracool dwarfs.

    The researchers detected radio emission from three of the 15 observed sources, including the detection of a new source, 2MASSW J0004348–404405. The emission from these three sources showed no variability or burst emission and was consistent with emission from a gyrosynchrotron mechanism. To characterise the magnetic conditions responsible for the observed radio emission, the team constructed a simple stellar magnetospheric model consisting of mildly-relativistic electrons that spiralled in a uniform magnetic field. They found the observed quiescent emission to be consistent with radio emission expected from a magnetic environment with a field strength 10 – 230 G and electron density 104 – 108 cm-3. Additionally, they analysed the general trends of the radio emission for this sample of 15 sources and found that the radio activity increased for later spectral types and more rapidly rotating objects.

    Publication details:
    Christene Lynch, Tara Murphy et al. in MNRAS (2016): Radio detections of southern ultracool dwarfs

    See the full article here .

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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

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  • richardmitnick 9:33 pm on January 20, 2016 Permalink | Reply
    Tags: , , CAASTRO, Simulated galaxy clusters show complexity of identifying centre   

    From CAASTRO: “Simulated galaxy clusters show complexity of identifying centre” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    9 December 2015 [Just now brought forward in another article by reference]
    No writer credit found

    Cosmological structure formation models assume lower mass systems to merge to form more massive structures, with galaxy clusters representing the final state of this process. These clusters are not only good cosmological probes but also valuable laboratories for testing models of gravitational structure formation, galaxy evolution, thermodynamics of the intergalactic medium and plasma physics. Observationally, galaxy clusters are usually identified through optical images, X-ray observations or gravitational lensing. A fundamental step in any of these procedures is the identification of the cluster centre though, and the preferred measures depend on the signal used. For instance, the minimum of the gravitational potential (which expects to define the centre if the cluster is in dynamical equilibrium) is usually adopted when using strong and weak lensing, whereas luminosity peaks are common measures when using optical and X-ray images. In a new publication by CAASTRO members Dr Weiguang Cui and Prof Chris Power (both at ICRAR-UWA) and colleagues, the researchers employed simulations to determine the difference in the estimation of the centre of a galaxy cluster when assuming different mass distribution and physical processes.

    Temp 1

    They created a statistical sample of clusters drawn from a suite of cosmological simulations in which they explored a range of galaxy formation models: Dark Matter only, CSF (hydrodynamical models that include gas cooling, star formation and supernova feedback) and AGN (feedback from supermassive Black Holes included in addition to CSF). The team investigated how the location of the galaxy cluster centre was affected by the choice of these observables. What they found was that the “brightest cluster galaxy position” from the optical images correlated more strongly with the minimum of the gravitational potential than the X-ray defined centres. The feedback from supermassive Black Holes, on the other hand, significantly enhanced the offset between the peak X-ray luminosity and the minimum gravitational potential. These results highlight the importance of identifying the cluster centre when interpreting cluster observations, in particular when comparing theoretical predictions and observational data.

    Publication details:
    Weiguang Cui, Chris Power et al. in MNRAS (2015): How does our choice of observable influence our estimation of the centre of a galaxy cluster? Insights from cosmological simulations.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

    PARTNER LINKS

    The University of Sydney
    The University of Western Australia
    The University of Melbourne
    Swinburne University of Technology
    The Australian National University
    Curtin University
    University of Queensland

     
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