10th June 2008
Marsfield Lecture Theatre

Programme

Abstracts
 
 

Joris Verbiest, Swinburne University of Technology

Long-term Timing of Millisecond Pulsars and Gravitational Wave Detection

Hundred years after the development of General Relativity, one of its key predictions - the existence of gravitational waves (GWs), is yet to be confirmed. The ATNF-led Parkes Pulsar Timing Array (PPTA) project has sparked international interest in trying to detect these elusive waves through precise timing of millisecond pulsars (MSPs). Besides the GWs themselves, the main unknown factor dictating the success of the PPTA, is the implicit (in)stability of MSPs, which hasn't yet been studied rigorously, mostly because MSPs were only first discovered 26 years ago.
In this talk, I will present the first large-scale (20 MSPs) investigation into long-term (~14 years) timing of MSPs. I will show the wide variety of stability that exists in the current PPTA sample of pulsars and comment on ongoing improvements and the feasibility of a GW detection in the short to mid-term future.
 
 

Daniel Yardley, University of Sydney 

Sensitivity of Pulsar Timing Arrays to Individual Sources of Gravitational Waves.

We present the sensitivity of the Parkes Pulsar Timing Array to single sources of gravitational waves. We also present simulation results demonstrating the sensitivity of future pulsar timing arrays. The single sources of gravitational waves are assumed to be supermassive binary blackholes (with member masses ~109 solar masses). The sensitivity curves obtained for current data, combined with a lack of detection of gravitational waves in all data sets to date, is being used to constrain the rate of coalescence of such objects.

Nadia Lo, University of New South Wales

Principal component analysis of multi-molecular line data

Following the MOPS upgrade, over 20 molecular line data cubes of a southern giant molecular cloud complex - G333 were obtained. With this large data set, various analytical methods, such as clump finding, principal component analysis (PCA) were applied to characterise the physical and chemical properties of the region. PCA provides a systematic way to look for similarity and differences among molecules in velocity and spatial dimension. For an example some molecules are tend to be detected along each other and some are not, hence help us to understand the chemical properties and velocity structure of molecular clouds.

Rajan Chhetri, University of New South Wales

An update on search for gravitational lenses in the Southern Hemisphere

Attila Popping, Kapteyn Astronomical Institute

The Simulated HI Sky

Future telescopes like ASKAP and the SKA will carry out much larger and deeper HI surveys than are possible today. Since such surveys are strongly limited by sensitivity, large HI galaxy samples beyond a recession velocity of even 3000 km/s and imaging of regions with column densities below log(NHI)~18 are almost unconstrained observationally. In order to calibrate our expectations and science goals with these new instruments, it is vital to use all available constraints on galaxy populations and diffuse gas topology at our disposal. SPH simulations give predictions of structure formation and the associated gas content and topology which embody much of our current knowledge, although clearly limited by both the incomplete physics and our current computational capacity. Such simulations at least attempt to represent a self-consistent system of dark matter, star and gas "particles" consistent with both cosmological constraints and a realistic interaction history. We will show a method to extract the HI gas from SPH-simulations, that in the first instance contain only the total baryon budget and mass-averaged physical conditions. This method is applied to a 32^3 Mpc SPH-cube evolved to the current epoch and is used to determine the implied HI mass function and HI distribution function down to extremely low column densities. These will be compared to existing HI surveys.

Kate Randall, University of Sydney

Discriminating between AGN and star forming galaxies in ATLAS

The Australia Telescope Large Area Survey (ATLAS) is the widest deep radio survey ever attempted, covering 7 square degrees of sky in two separate fields, with extensive complementary data. The primary aim of my research is to investigate all possible discriminants between active galactic nuclei (AGN) and star-formation (SF) in ATLAS, with the goal of comparing discriminants, identifying the strengths and weaknesses, and establishing an optimum technique given the available data. Ultimately, all possible discriminants will be utilized, including optical/infrared SEDs, spectroscopic line widths, optical line ratios, radio spectral indices, variability, morphology, polarization and the radio/FIR correlation.

Minnie Mao, University of Tasmania

Cosmic Evolution of Radio Sources

The Australia Telescope Large Area Survey (ATLAS) aims to image about seven square degrees of sky in two fields, making it the widest deep field radio survey ever attempted. One of ATLAS\u2019s primary goals is to determine how galaxies formed and evolved through cosmic time. My role in ATLAS is to investigate evolution in AGN by studying how their spatial structure and properties change over cosmic time. In my talk I will first outline my PhD project, then go on to discuss some of the work I have completed so far.

Christopher Hales, University of Sydney

Unveiling Cosmic Magnetism Using ATLAS

Magnetic fields play a fundamental role in many astrophysical phenomena, but the origin, evolution and structure of such fields still remain unsolved problems in astrophysics. Did significant primordial fields exist before the first stars and galaxies? If not, how and when were magnetic fields subsequently generated? In this introductory talk I will discuss my PhD plans to use the Australia Telescope Large Area Survey (ATLAS) to investigate the role of magnetic fields in controlling how galaxies form and evolve, so as to shed light on these important questions.

Ann Mao, Harvard University

A Rotation Measure survey towards the Galactic Caps

Coherent large-scale magnetic fields have been observed in the Milky Way and other normal spiral galaxies. The favored field amplification mechanism is the dynamo theory, which relies on turbulent gas motions and the differential rotation of the galactic disk. Unfortunately, details of the dynamo mechanism are still not yet well understood. The parity and the strength of the vertical magnetic field is the key to understand Galactic magnetism, but these quantities are poorly constrained. To detect and map the vertical field of the Galaxy, we have carried out a survey of Faraday rotation toward 500 polarized extragalactic sources behind each of the North and South Galactic Poles, carried out with the WSRT and ATCA, respectively. We will present the first results from these observations, and show how they can provide a complete characterization of the Milky Way's vertical magnetic field structure at our location in the Galaxy.

Anne-Marie Brick, University of Tasmania

Galactic Structure and Methanol Masers

Methanol masers are compact objects which occur close to high-mass star forming regions and thus lie in the spiral arms of the Galaxy. They emit at radio wavelengths and hence can be observed through the gas and dust which obscures radiation at optical wavelengths. Their compact and intense nature makes them prime candidates for astrometric observations which are currently the most direct and accurate way of measuring Galactic distances and source proper motions. Very Long Baseline Interferometry (VLBI) will be used to obtain the high-resolution observations needed to measure parallax in objects at kiloparsec distances (such as masers) and can also be used to accurately measure the proper motion of the masers. Combining the proper motion, distance and the line of sight velocity, a three-dimensional view of the regions surrounding the masers can be obtained. The high resolution proper motion observations obtained with VLBI are also the perfect tool for investigating high-mass star formation processes such as detecting infall into these regions.

Aaron Chippendale, University of Sydney

Towards Measuring Reionization at Large Scales in 21 cm

I will give an update on the Cosmological Reionization Experiment (CoRE). This will cover the design of a specialized telescope, operation at the Radio Quiet Zone in WA, and what we have learned from the results. The goal is to develop techniques for measuring the 21 cm reionization monopole. That is the mean redshifted 21 cm line over all lines of sight. Evolution of the 21 cm monopole with redshift traces reheating and reionization of the intergalactic medium that is coincident with galaxy formation. Successful observations could identify the nature of the first stars and test theories of structure and galaxy formation.

Elizabeth Mahony, University of Sydney

Radio-Loud QSOs in the AT20G Survey

Until recently, the radio sky at frequencies above 5 GHz was largely unexplored. The Australia Telescope Compact Array 20 GHz (AT20G) Survey is the first comprehensive high frequency radio survey and provides valuable information about the early stages of active galaxy evolution as well as being vital for future CMB missions such as Planck. My PhD project involves working with the AT20G team and in particular studying the optical components of these sources. From preliminary results we know that 74% of these sources have optical counterparts, the majority of which are quasars.

Leith Godfrey, Mount Stromlo

VLBI Imaging of a Luminous X-ray Hotspot

Abstract: VLBI imaging of the z=0.662 broad line radio galaxy PKS1421-490 reveals a compact hotspot with peak radio surface brightness ~400 times greater than the hotspots of Cygnus A. The hotspot X-ray luminosity is more than an order of magnitude greater than any other hotspot observed with Chandra. We successfully model the radio to X-ray spectral energy distribution using a one-zone synchrotron self Compton model with a near equipartition magnetic field strength of 3 mG, confirming the special status of equipartition field strengths in high luminosity hotspots. The hotspot radio spectrum flattens significantly at low frequencies. We model the flattening by incorporating a cut-off in the electron energy distribution at gamma_min ~ 650. Such a cutoff requires the that jet have a significant proton component and bulk Lorentz factor Gamma > 5.

Paul Hancock, University of Sydney

What I learned from the 4th CSS/GPS conference in Riccione.

One of the goals of my thesis is to investigate the Gigahertz Peaked Spectrum (GPS) radio sources that appear in the Australia Telescope Comapct Array 20GHz survey (AT20G). Recently I attended the 4th CSS/GPS conference in Riccione to present my work. In this talk I will give an outline of the work that I have done and how it fits into our current understanding of GPS sources. I will also give an overview of the current understanding of Compact Steep Spectrum (CSS) and GPS sources.

Keith Bannister, University of Sydney

Archival and Future Searches for Radio Transients

Since the discovery of pulsars in 1967, transient, variable and pulsing radio sources have been a subject of intense interest in radio astronomy. The recent discovery of a 1ms, 30 Jy transient in archival Parkes data has, among many other recent discoveries, increased interest in mining existing data for interesting objects, as well as stimulating new searches for transient emission. My project is twofold: a search through the Molonglo Observatory Synthesis Telscope (MOST) archive for transient and variable objects, and the design, implementation and use of a transient survey instrument using the 6 antenna ASKAP engineering model, Beta. The vast computing resources afforded by ASKAP enable the exciting prospect of imaging and de-dispersing several million pixel image every millisecond, ushering in a new regime in wide field transient searches.