Research
My research interests are wide and varied. Below is a brief list of some of them with a description of each.
Cosmology - Friedmann equation and space-time metrics
Cosmology is the study of the Universe as a whole. Cosmology uses the Friedmann equation and metrics such as the Friedmann-Robertson-Lemaitre-Walker (FRLW) and Minkowski metrics to describe the geometry of space time and it's evolution. The Friedmann equation simplifes the Universe by treating each component of the Universe as homogeneous, isotropic fluids that don't interact. This is a valid approximation to first order, but in practise it breaks down. The distribution of matter and energy in the Universe is `clumpy', not smooth. I'm interested in extensions of the Friedmann equation and space-time metrics that allow for this clumpiness and incorporate it as a feed-back term.
Cosmology - Dark energy
Dark energy was discovered in 1999 by two teams that were studying the distances to Type IA Supernovae. Type IA Supernovae are exploding white dwarf stars whose luminosity can be calibrated from their light curves. Using their luminosities the distances to these Type IA Supernovae can be calculated for an assumed cosmological model. The distances to the Type IA Supernovae where further away than expected, which revealed that the Universe's expansion was accelerating. The best explanation for this accelerating expansion is the existence of dark energy. We know very little about dark energy. To study dark energy we treat it as a homogeneous, isotropic fluid and parametrise it's equation of state by the parameter w(z), which is allowed to vary with time. I'm interested in theoretical models of dark energy, ways to parametrise the dark energy equation of state and it's evolution, measurements of w(z) and novel tests to differentiate between dark energy models.
Source finding
Automated source finding is crucial to the success of large surveys. Manual source finding takes too long to be feasible for large surveys such as SDSS, GALEX MIS, WISE and WALLABY. I'm currently developing source finders that detect emission sources in the high spectral resolution datacubes that come from Australian Square Kilometre Array Pathfinder (ASKAP) observations. Currently, I'm developing a source finder that uses the Kuiper test (a modified version of the Kolmogorov-Smirnov test) to identify regions of a spectral datacube that aren't noise-like.
Galaxy Evolution
Coming soon.
Red Quasars
Red Quasars were discovered in the 1990s. Red Quasars are the result of either excess synchrotron emission or dust intrinsic to the Quasar that reddens the spectral energy distribution. If red Quasars are the result of reddening by intrinsic dust, then red Quasars are a potential evolutionary link between Ultra Luminous Infrared Galaxies (ULIRGs) and blue Quasars. This possible evolutionary pathway is why it's important to identify the mechanism that creates red Quasars.
Databases
Astronomy and particle physics both face the problem of `data deluges', where data arrives faster than it can be examined and interpreted. Databases allow us to deal with data deluges by storing data in a meaningful way as it arrives, so that it doesn't have to be processed on the fly. I'm interested in developing sparse representations of astronomical sources for databases. This will allow more precise data to be stored for an object than currently is. Current astronomical databases only store macroscopic properties such as total flux, position and size. They get around the limitations of storing macroscopic properties by storing many variations of each macroscopic property (such as total flux measured for multiple apertures). I'm also interested in developing novel approaches for efficiently searching indexed and non-indexed or partially sorted data.
Analytic proof of the four colour map theorem
The four colour map theorem is an intriguing mathematical problem. In the 1800's a boy was given a map of the world for Christmas. He discovered that he could colour in the map using just four colours, without any two countries that shared a border having the same colour. He asked his older brother if this was possible for all maps. His brother was attending university and asked his mathematics lecturer. This mathematician found that for every map he could indeed colour it with just four colours. Over the next ~200 years many attempts were made at finding an analytic proof for. In the 1960's the four colour map theorem was proven by example and exhaustion using computers. It was shown that all maps can be constructed by stitching together maps from a set of ~1400 (Originally it was a base set of ~2000 maps, but over the years it's been reduced to a smaller set.). By proving that each map in this base set could be coloured using just 4 colours, it demonstrates that every map can be coloured using just 4 colours. I'm interested in trying to solve the four colour map theory analytically by treating it as an energy minimisation problem.
Quasar variability
Radio galaxies, Quasars, Seyfert galaxies, Blazars and Liners can be related to each other using the unified model of active galactic nuclei (AGN) galaxies. In the AGN unified model, all of these galaxies are the same physical system but viewed at different distances and different orientations. AGN galaxies are galaxies with a black hole at the centre with material accreting onto it. This accreting material heats up and emits light and also couples to the black holes magnetic field to drive collimated emission jets. Quasar variability provides information on the regions of the accretion disk and jets that are responsible for emission at different wavelengths. Studying Quasar variability might allow us to constrain models of black holes, accretion disks and emission jets.
Galactic, intergalactic and intrinsic dust
Electromagnetic radiation from space is viewed on Earth after it's passed through galactic dust in our own galaxy, intergalactic dust between galaxies and dust intrinsic to the galaxy emitting radiation. In order to correct the flux for the effects of dust, we need to understand the constitution and distribution of this dust to model its effect on radiation passing through. I'm interested in using integral field spectroscopy and millimetre radio observations to map out the constitution and distribution of dust in galaxies.
Projects & Surveys
Astronomy & astrophysics has entered an era where technology allows increasingly larger, deeper more detailed surveys of the sky to be carried out. This is a list of the large-scale astronomical projects/surveys that I'm affiliated with and my contribution.
Fornax cluster Complete Spectroscopic Survey (FCSS)
The FCSS is a blind spectroscopic survey of bj
WiggleZ Dark Energy Survey (WiggleZ)
The WiggleZ survey is an ambitious 220 night project that was carried out using the AAOmega spectrograph on the AAT. Using AAOmega and the AAT, spectroscopic redshifts were obtained for ~240,000 emission line galaxies across ~1,000 sq. degrees of sky, that were selected from a combination of GALEX, SDSS and RCS2 data. Analysing the spatial distribution of these galaxies, we have identified a characteristic separation between the emission line galaxies. This characteristic separation is the imprint of Baryonic Acoustic Oscillations (BAOs), which are sound waves in the early Universe, in the spatial distribution. We know the physical size of this characteristic separation so we can use simple trigonometry to calculate the distance to these galaxies as a function of redshift. This allows us to measure the distance-redshift relationship and fit for the cosmological parameters that describe our Universe. Using the cosmological parameters obtained from analysis of the distribution of temperature fluctuations in the Cosmic Microwave Background (CMB), we can fit a model of the Universe's expansion to our distance-redshift relationship to determine the remaining cosmological parameters describing dark energy, which have a negligible effect on the CMB. I helped with the survey design, measurement of the selection function and luminosity function, observing, redshifting and developed pipeline software that was used to carry out the survey. I was also responsible for carrying out the WiggleZ pilot survey.
The WiggleZ survey's public webpage
Wide-field ASKAP L-band Legacy All-sky Blind surveY (WALLABY)
WALLABY is one of the two top-ranked surveys that will be carried out using the ASKAP radio synthesis telescope. It will search for the radiation emitted by neutral Hydrogen gas over ~70% of the sky at phenomenal spatial and spectral resolutions of 30\" and 4 km/s, respectively. It will be able to detect the 21cm/1.4GHz line emitted by the spin flip of neutral Hydrogen atoms out to a redshift of 0.2, but the majority of sources will be at redshifts less than 0.05. The key to realising the WALLABY survey is the massive 5 x 5 degree field of view of ASKAP, which is made possible by the use of Phased Array Feeds (PAFs). The unique difference between radio surveys like WALLABY and spectroscopic surveys in the optical or infrared, is that it is a truly blind survey. Blind optical and infrared spectroscopic surveys are limited to obtaining spectra for a limited number of sky positions at any one time, so a blind survey is the same as saying it's a random sampling of the available targets. Radio spectral datacubes, like those that WALLABY will obtain, contain spectra for every single point of sky that is within the telescopes field of view. This means that spectroscopic radio surveys like WALLABY are truly blind surveys. This means that WALLABY has tremendous capacity for serendipitous discovery, and we can determine not only where neutral Hydrogen gas is located, but also where there isn't any. The combination of large sky coverage, high resolution and true blind nature will make WALLABY a tremendous astronomical dataset. I am involved with developing a source finder for WALLABY and along with Dr. Chris Fluke at Swinburne University co-manage the technical working group responsible for WALLABY databasing, cataloguing and visualisation.
The WALLABY survey's public webpage
Westerbork Northern Sky HI Survey (WNSHS)
The WNSHS will complement WALLABY by obtaining coverage of the north polar cap, that is inaccessible to ASKAP from Western Australia. This survey will be carried out using the new Vivaldi design aperture arrays that are being installed on the Westerbork radio synthesis telescope. The WNSHS will have comparable depth and resolution to WALLABY. In combination with WALLABY, WNSHS will greatly improve the science that could be done with either survey alone. For example, the two surveys in combination will be able to measure the Tully-Fischer relation to much better precision and accuracy than either could alone.
Deep Investigation of Neutral Gas Origins (DINGO)
Like WALLABY, DINGO is going to detect the emission of neutral Hydrogen gas using the ASKAP radio synthesis telescope. The difference between the two is that while WALLABY is a relatively shallow survey that covers most of the sky, DINGO will be going very deep over a small region of the sky. The two surveys complement each other very well, and is an example of the `wedding cake' approach to surveys that astronomers often refer to. DINGO will observe 3-4 fields to different depths, with their deepest field detecting 21cm emission out to a redshift of z ~ 0.4. DINGO will be a fantastic resource for combining with other existing galaxy surveys, to provide information on neutral Hydrogen content for more than 100,000 galaxies. I am involved with the development of a DINGO source finder.