Descriptions of Current PhD Research

Joris Verbiest - Long Term Pulsar Timing and Tests of General Relativity

Millisecond pulsars are among the heaviest compact objects in the Universe. On top of that, they are also the most stable clocks known, with spin periods typically stable to one part in 10^-14 over years or even decades. The technique that uses this incredible stability to probe the environment and behaviour of these exotic objects, is called "Pulsar Timing".

For my Ph.D. I am now analysing pulsar timing data taken at the Parkes Radio Telescope over the past ten years. Since most millisecond pulsars were only discovered in the 1990's, such data sets are equally rare as valuable: they are exquisite tools for measuring the distances to and masses of the pulsars, amongst others. Perhaps the most exciting part of this analysis is that it leads the way to the detection of gravitational waves, as part of a larger Pulsar Timing Array project.

Emil Lenc

My PhD research involves the application of new wide-field, high spatial resolution radio imaging techniques to observations of starburst galaxies and radio galaxies. These techniques enable me to measure the expansion speeds of supernova remnants in starburst galaxies and so infer the epoch of the supernova explosions. By observing many supernova remnants I can piece together the star formation history of the galaxy and examine how the galaxy has evolved with time. Wide-field radio imaging techniques also provide a means to observe the interaction of radio galaxy jets as they propagate through a galaxy. My observations can help constrain theoretical models of X-Ray emission mechanisms in jet interaction regions as well as determine fundamental properties of the jets such as their speed and kinetic power. I work with Prof. Steven Tingay (Curtin), Dr. Tim Cornwell (ATNF) and Dr. Tasso Tzioumis (ATNF).

Adam Deller - The development of a distributed software correlator, and its application in Very Long Baseline Interferometry (VLBI) to pulsar astrometry

I study the kinematics of pulsars using VLBI astrometry to determine parallaxes and proper motions, and hence distances and transverse velocities, of Southern pulsars using the Australian Long Baseline Array (LBA). VLBI astrometry provides the only way of obtaining model-independent distance measurements to pulsars in the celestial reference frame, and as such is crucial for properly calibrating pulsar luminosities, testing GR and other interesting astrophysics.

VLBI has undergone a rapid transition recently with the upgrade of tape media based systems to disk. This process was completed in the LBA in 2006, necessitating a replacement for the tape-based S2 hardware correlator. This leads to the other face of my research, which is astrophysical instrumentation. I have written a software correlator which runs on the Swinburne supercomputer, which is used to correlate LBA experiments.

Tim Connors - High Resolution simulations of Galactic Cannibalism

I am attempting to model the Magellanic Stream and High Velocity Clouds (HVCs), using N-body simulations. Our Magellanic Stream work includes N-body gravitational physics and we have preliminary results using gas physics -- most notably, drag and star formation. In our HVC work, we use fully cosmological simulations in order to be able to find whether our simulations, and hence, our modern knowledge of astrophysics, can naturally explain the existence of these mysterious anomalous velocity clouds around the MW, and indeed whether HVCs can be expected to be found surrounding most other disk galaxies too.

I use our own parallised SPH simulation code, GCD+, on the three major academic supercomputers in Australia, including Swinburne's, and compare the simulations against HIPASS cubes from the Parkes telescope using a variety of in-house data analysis and 2 and 3D visualisation tools.

Alyson Ford - The Origin and Nature of HI Clouds in the Lower Halo of the Galaxy

Faint, discrete HI clouds near the Galactic plane have recently been observed using the Green Bank Telescope (Lockman, 2002). Distances to these clouds can be determined by looking towards tangent points of the inner Galaxy at velocities expected from Galactic rotation. This provides a huge advantage over most HI clouds by allowing us to determine their physical properties such as size and mass. I am using data from the Galactic All-Sky Survey (GASS), an HI survey obtained using the Parkes Radio Telescope over the past two years, to create a complete inventory of such clouds, along with a statistical evaluation of their physical properties. These clouds are quite abundant and may be responsible for a considerable amount of HI mass in the lower halo. Since these clouds are not gravitationally bound, the issue of their stability will be explored, along with an analysis of their spatial distribution. Also, by comparing the distribution to various Galactic components such as supershells and HII regions, I will determine the likelihood of such clouds being generated in these environments.

To further explore the possibility that these clouds formed as a result of the evolution of a superbubble, either as clumps of HI that have been pushed up from the disk during the blowout or fragments of the cap that have condensed into cool clumps, I have performed 3D hydrodynamic simulations of the evolution of a superbubble using Fyris, a program developed by Ralph Sutherland (ANU).

Lee Spitler - Imaging of Globular Cluster Systems

Globular clusters are among the densest stellar entities in the universe and can contain up to a million stars. Most formed roughly 10 billion years ago, when galaxies were only just beginning to form. A given galaxy's globular cluster system therefore provides an important observational probe of the earliest stages of galaxy formation.

I study optical (e.g. HST) to mid-infrared (e.g. Spitzer) imaging of extragalactic globular cluster systems. By characterizing the spatial, color, and luminosity distributions of globular cluster systems as functions of both host galaxy type and environment, we provide observational constraints on early galaxy formation.

Image Caption: This is a close-up of the latest dataset I've worked with. It is the result of a successful telescope proposal to use the Suprime-cam imager on the 8-m Subaru telescope in Hawaii. While the quality of this web image doesn't give the real data justice, you can still see globular clusters in the giant elliptical galaxy NGC 1407 (big source of light on the left) as the faint, bluish dots on this image.

See my website for more details: http://lee.spitler.googlepages.com/research

Paul Kiel - Populating the Galaxy with Pulsars

The majority of pulsar population synthesis studies performed to date have focused on isolated pulsar evolution. Those that have incorporated pulsar evolution within binary systems have tended to either treat binary evolution poorly or evolve the pulsar population in an ad-hoc manner. Here I am working on producing the first model of the Galactic field pulsar population that includes a comprehensive treatment of both binary and pulsar evolution. Synthetic observational surveys mimicking a variety of radio telescopes are then perfomed on this population. As such, a complete and direct comparison of model data with observations of the pulsar population within the Galactic disk will soon be possible. The tool used for completing this work is a code (work in progress) comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects.

Annie Hughes - Cold gas and dust in the Large Magellanic Cloud

Our neighbouring galaxy the Large Magellanic Cloud (LMC) presents a unique opportunity at an entire galaxy at high angular resolution. A gas-rich dwarf irregular galaxy with clear signs of active star formation, the LMC is an excellent laboratory to investigate the relationship between different phases of the interstellar medium (ISM), the interaction of the ISM with individual objects, and the influence of galactic-scale processes on the properties of interstellar material.

For my thesis, I'm investigating two problems relating to processes in the interstellar medium: the origin of the global radio-FIR correlation, and the formation of molecular clouds out of the ambient atomic gas. To address these questions, I'm conducting a high resolution survey of the 12CO(J=1-0) emission from the molecular clouds in the LMC using the ATNF Mopra telescope. I'm also using archival data from recent surveys of the LMC by the Spitzer Space Telescope and the Australia Telescope Compact Array.

Andrew Green - Distant and Nearby Galaxy Survey

I'm working on a survey of both distant and nearby galaxies using 3-D spectrographs on Gemini and the AAT. These new instruments take a spectrum at each pixel location in an image, thus allowing greatly enhanced understanding of the properties of galaxies, particularly the dynamics, across their entire projected image. These data will be used to draw conclusions about galaxy formation and evolution, and the cosmology of small dense regions. My other interests are teaching, public outreach, and gravitational weak lensing, where my collaborators and I have completed one of the first galaxy cluster catalogues selected entirely by weak lensing. Ultimately, this technique will allow for a better understanding of the evolution of large scale mass distributions in the universe.

Trevor Mendel - The Anatomy of a Galaxy Group

Galaxy Groups are among the most common structures in the observable universe, yet our knowledge of the specific processes acting there is limited. Given recent observations suggesting that galaxies are "pre-processed" in groups prior to entry into clusters, a more detailed study of the group environment is called for. For my Ph.D. I have obtained multi-object spectra of the NGC 5044 group using the AAOmega instrument at the Anglo-Australian Telesope. These spectra are high enough quality to not only spectroscopically confirm a significant number of galaxies as group members but also perform a detailed analysis of their stellar populations, looking at details of their star formation histories and clues to galaxy evolution in the group environment.

Aquib Moin - e-VLBI science with the LBA and explorating science applications for the long baseline component of ASKAP

This PhD project is partly aimed at contributions to the technology development of e-VLBI in Australia and partly aimed at obtaining scientific return from e-VLBI with the systems that are developed. The science component of this project will focus on the observation of radio sources associated with Gamma-ray Bursts (GRBs) and Galactic X-ray binary systems.

The technical activities include the development of streamlined software to carry out the e-VLBI operations for targets of opportunity appearing at short notices. This also involves the development of an automated alert system that communicates the candidate trigger information to assess its potential to be observed using e-VLBI. This alert system will be based on the transient alert systems from the space-based X-ray and Gamma-ray observatories.

Observations of the radio emission associated with X-ray binaries and GRBs using e-VLBI may return useful scientific outcome in terms of detection, monitoring and eventually the study of these mysterious phenomena. A long-term objective of this project is also to explore the transient detection capabilities of Australia's SKA demonstrator ASKAP, which is to be built in Western Australia.

This work is mainly being supervised by Prof. Steven Tingay (Curtin) and by Dr. Chris Phillips at the ATNF, and it will involve the three ATNF telescopes and also the Hobart telescope. The data analysis will mainly be done using AIPS.

Caroline Foster - Internal Properties of Early-type Galaxies

Past studies of the stellar content and kinematics of early-type galaxies have focused on either the underlying starlight near the galaxy centre or on globular clusters at large radii. Thus yielding an incomplete picture. Using data from the DEIMOS instrument on the Keck telescope, I will study the kinematics and stellar content through both the underlying starlight and globular clusters at radii yet to be explored. The properties will then be compared to the predictions from galaxy formation models.

Andrew Butler - Galaxy Evolution as a Function of Environment and Cosmic Time

It has been known for some time that galaxy evolution is a function of environment. The densest and most interesting of environments are galaxy clusters, which are among the most massive gravitationally bound structures in the universe. It is thought that the most massive and luminous galaxies in the universe, which are early type ellipticals and mostly reside in the dense centers of clusters, formed relatively early in the history of the universe via the process of hierarchical merging (i.e. galaxy collisions). It has also been known for some time that the fraction of blue late type galaxies in clusters, which mostly reside in the less dense outer regions, increases with higher redshift (known as the Butcher Oemler effect). This means that the star formation in galaxies falling to the center of clusters has been suppressed somehow over the history of the universe. For my thesis I am investigating the mechanisms behind this phenomenon using optical data of galaxies in clusters in a wide range of redshifts to determine their evolution, both spectroscopically and morphologically, as a function of environment and redshift. Since radio jets that emanate from the elliptical galaxies and heat the interstellar medium, thus preventing star formation, are becoming increasingly evident, I also use radio data to investigate the connection between radio emission and star formation suppression. My studies should allow insight into the link (or lack thereof) between the morphology-density relation, the Butcher Oemler effect, the processes responsible for the termination of star formation in galaxies, and the relative importance of major merging events between clusters.

Image Caption: This is an HST WFPC2 mosaic of the central regions of galaxy cluster MS1358+62, which is at a redshift of z=0.328. We have proposed to observe the spectra of the blue galaxies in order to measure their mass (from their rotation curves), which should allow us to determine whether they are the progenitors of S0 galaxies or of the dwarf galaxy population in low-redshift rich clusters.