The Pan-Andromeda Archaeological Survey (PAndAS)


How did our extra-galactic companions evolve? PAndAS seeks to understand the process.


Professor Geraint F. Lewis

Research Location

School of Physics

Program Type



How do galaxies grow over cosmic time? Historically, to answer this question, astronomers have peered into the depths of space to try and see galaxies in formation, but recently it has been realised that we should be surrounded by the archaeological evidence, in terms of old stellar streams and dismembered dwarf galaxies, that will allow us to piece together the our own formation history. Unfortunately, residing inside our own Milky Way distorts and limits our view, and we have to turn to our nearest extra-galactic companions, the Andromeda and Triangulum galaxies, to try to identify the signatures of their formation history. The goal is to see the individual stars in the outer reaches of these galaxies, and map their properties to reveal their history. But the halos of these galaxies cover a huge area of sky and historical methods, such as film photography, as simply not sensitive enough to achieve the goal.

Recently, however, technological advances have allowed us to take a new look at our extra-galactic companions, with the Pan-Andromeda Archeological Survey (PAndAS) providing the first exquisite analysis of a huge swathe of sky encompassing the Andromeda and Triangulum galaxies using sensitive, large format CCD detectors (in this case, MegaCam on the Canada-France-Hawaii Telescope). The results, so far, have been spectacular, revealing shreds of dismembered galaxies that are being consumed as the larger galaxies grow. The project has several more years to run, with the complete data-set providing an entire census of stars in the halos of our nearest companions.

With this project, you will gain access to this massive data-set, identifying and characterizing the extensive tidal debris that accompanies the two large galaxies, and use data from large telescope to target the stars and measure their velocities. Armed with this information, you will develop a picture of how the tidal debris was formed, from what it came, and what it will become, while at the same time measuring the distribution of dark matter that enshrouds the large galaxies and dominates their motion. The overall goal will be to provide a calibration of the ongoing galaxy evolution within our local Universe and relate that to our understanding of galaxy formation as a whole.

With this project, as well as gaining a working knowledge of the key topics in galaxy formation and evolution, you will further gain the skills of working with massive data-sets and computer models of galaxy interactions. PAndAS is a large, international collaboration with strong support for its members, especially students, and it is envisaged that collaboratory visits with key researchers will be available during the project. Furthermore, the project should yield a series of key results which you will publish as part of your candidature, leading to a thesis by publication.

Additional Information

The student will be a member of the Gravitational Astrophysics Group at the Sydney Institute for Astronomy ( This group provide strong peer support for students throughout their candidature.

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physics, galaxy, galaxies, cosmology, galactic evolution, observational astronomy

Opportunity ID

The opportunity ID for this research opportunity is: 906