Potential research projects

Simulating High Angular Resolution Observations with the Square Kilometre Array. (PhD/Masters/Honours)

The high angular resolution component of the Square Kilometre Array (SKA) will have sensitivity that is orders of magnitude better than current Very Long Baseline Interferometry (VLBI) arrays, and will open up a vast array of scientific opportunities. In order to inform design decisions for the SKA, simulations of various proposed experiments must be performed. This project will involve simulating high angular resolution SKA observations of proto-planetary disks, AGN jets, star-bursts, and/or other objects of interest using high performance computing platforms (such as Curtin's CUPPA cluster), and developing efficient imaging and calibration techniques, again using parallel computing capabilities. This project will enable the candidate to get involved in the early design stages of the Square Kilometre Array project, develop an excellent understanding of radio astronomy techniques, and develop skills in high performance computing that could be applied in industry and other non-academic jobs. The project may be extended to include observational and theoretical work that would help to improve source models to be incorporated into the simulation package. The scope of this project can be modified to fit the requirements for an honours, masters or PhD program.

An investigation into the X-ray emission mechanism and dynamics of large-scale quasar jets (Honours)

Background

Active galaxies are a class of galaxy in which a significant fraction of the radiated energy is associated with a small bright region at the galactic centre, known as an "active galactic nucleus", or AGN. The radiation from AGN is believed to be the result of accretion of matter onto a supermassive black hole at the centre of the host galaxy. A sub class of active galaxies, known as radio galaxies, produce highly collimated beams, or jets, of relativistic magnetized plasma that emit strongly at radio wavelengths, and travel at close to the speed of light. In some cases the jets extend several million light years from the host galaxy, making them the largest known objects in our universe. The scales involved and the energy associated with radio galaxies are truly incomprehensible, and their images are some of the most beautiful and intriguing in all of astronomy. Radio galaxies are a fascinating phenomenon worth studying in their own right, but the study of radio galaxies also has a much broader context: The energetic jets of relativistic plasma ejected from active galactic nuclei have a strong and lasting impact on their host galaxies and the surroundings, and they regulate the growth of the central super-massive black hole.

Extragalactic jets have been studied for over four decades, but they are only superficially understood. Many fundamental issues remain unresolved, including what is the jet composition? and how are the jets produced? The general paradigm, that jet production is linked to accretion onto a supermassive black hole, is widely accepted. However, a number of proposed jet production mechanisms remain viable. The jet composition has significant implications for the jet production mechanism: Jets powered purely by an accretion disk are expected to be primarily composed of normal matter (protons and electrons), while jets powered by the rotational energy of the supermassive black hole are expected to contain mostly electron/positron pairs. A first step towards addressing these fundamental questions will be to understand the emission mechanisms and dynamics of large-scale extragalactic jets.

In the mid-1990s several hundred extragalactic jets had been observed at radio wavelengths, but only a handful of the nearest and brightest jets had been detected at X-ray wavelengths. The Chandra X-ray Observatory was launched in 1999, and with its incredible sensitivity and resolution, this observatory started of a new era in the study of extragalactic jets. Chandra's very first observation produced an amazing discovery: The quasar PKS 0637-752 was believed to be a moderate strength point source at X-ray wavelengths, and was therefore used for focusing Chandra's mirrors. However, these very first calibration observations revealed a surprisingly strong X-ray jet extending far from the quasar core. The strong X-ray emission from this large-scale jet was hard to explain in terms of standard emission mechanisms, and new models were quickly proposed. However, these new models also face serious problems, and more than ten years on, the question remains: what is the X-ray emission mechanism in the jet of PKS 0637-752, and other X-ray bright extragalactic jets like it?? The answer to this question has implications for understanding a number of other fundamental questions such as the jet composition, and the speed and power of the large-scale jets.

In this honours project, we will address the question what is the X-ray emission mechanism in large-scale X-ray bright extragalactic jets by combining high angular resolution radio images with Chandra X-ray Observatory images of the prototypical X-ray bright jet: PKS 0637-752.

Objectives

We have high angular resolution radio data from the Long Baseline Array for the famous jet of PKS 0637-752. The initial goal of this honours project will be to produce a high angular resolution radio image of the PKS 0637-752 jet. This will be a great achievement in itself, since it will be one of the first images of a large-scale X-ray bright jet at such high angular resolution. The aim will then be to critically assess models of jet X-ray emission in light of the new data.

The student will have the opportunity to work with data from the Long Baseline Array, the Chandra X-ray Observatory, critique existing theoretical models, and/or develop new theoretical models.

Work Plan

This is an excellent honours project in astronomy / astrophysics because it contains both observational and theoretical aspects, so there is a very broad scope. As such, the project can be directed in consultation with student, and the relative amounts of data analysis and theory adjusted accordingly.

1. Develop an understanding of radio interferometry, with a particular emphasis on Very Long Baseline Interferometry (VLBI).
2. Calibrate the Long Baseline Array data, and produce the first VLBI image of the large-scale jet in PKS 0637-752.
3. (optional) Spatial modelling of Chandra X-ray Observatory data, based on the results of the Long Baseline Array radio data.
4. Consider the implications of our new radio data for the interpretation of the X-ray data. Specifically, we will address the question: do the new high angular resolution radio data favour a synchrotron or inverse Compton interpretation for the jet X-ray emission?
5. We have new ATCA observations scheduled for February 2012, which will further inform the theoretical models for this source.

References

Some background on radio astronomy, including radio interferometry, as well as some background on the synchrotron and inverse Compton emission mechanisms.

Harris, D.E., & Krawczynski, H., 2006, Annual Review of Astronomy and Astrophysics, Vol. 44, Issue 1, pg. 463–506

Worrall, D.M., 2009, The Astronomy and Astrophysics Review, Vol. 17, pg. 1–46.