Galaxies and their Evolution
In optical astronomy we are studying galaxy populations and their evolution using surveys of nearby galaxies to look for previously undetected low surface brightness and compact galaxies, and observations of more distant clusters and groups to look for evidence of the evolution of their galaxy content. The Fornax Cluster Spectroscopic Survey uses the 2dF multi-object spectrograph on the Anglo-Australian Telescope to measure redshifts for complete samples of objects detected in the direction of the Fornax Cluster, while the Hubble Space Telescope Treasury Survey of the Coma Cluster has used the HST to image the nearest extremely massive cluster at high resolution, in order to explore the galaxy population in such an environment in great detail.
Other galaxies work concentrates on both surveys of high-redshift star-forming galaxies and the multi-wavelength properties of individual sources. Redshift is a proxy for lookback time, hence we are exploring the first structures that formed in the Universe and the 'epoch of reionization', the era when photons from the first generations of stars and quasars ionized the universe.
Fig.1 shows the central two-degree wide area of the Fornax Cluster. The (negative) image emphasises the huge difference between normal sized galaxies (the large fuzzy objects) of the type you see in text books, and our newly discovered objects, which we have dubbed ultra-compact galaxies. The latter are the nearly invisible dots at the centres of the circles and the even fainter ones inside the squares.
Galaxies grow in size and complexity as the Universe evolves over time. Therefore, by looking at relatively simple systems at high redshift we can hope to form a picture of how the first galaxies formed and how they have evolved into the multitude of diverse systems we see at later times.
We attempt to study these systems over a range of wavelengths probing different physical processes in the host galaxies. By studying these systems from rest-frame ultra-violet to radio wavelengths, we can build a picture of their stellar, molecular gas and dust content. This allows us to determine the nature, star-formation history and subsequent fate of galaxies in the early Universe.
Having previously carried out pioneering work on the discovery and study of galaxies seen 1-2 billion years after the Big Bang, we are now exploring how galaxies such as these evolve in the subsequent several billion years, and how this evolution is affected by their environment. In particular we are exploring how proto-cluster environments (the progenitors of the massive galaxy clusters seen in the current-day universe) affect the properties of the galaxy populations within them. The studies are multi-wavelength in nature in order to characterise the full galaxy population and avoiding biases caused by selecting only certain types of systems.