Globular Cluster Systems

Globular clusters are thought to be the oldest radiant objects in the universe and orbit, usually in large numbers, around galaxies of all morphological types. As fossil remnants of the early environments, out of which galaxies formed, they are powerful probes of the processes of galaxy formation and evolution.

Unlike single stars, globular clusters can be observed far beyond our local group of galaxies, providing clues about the early histories of different types of galaxies. Because they are relatively simple stellar populations (at least chemically), they are more easily modelled and understood than the unknown mix of stars of different ages and chemical compositions that make up the diffuse stellar population of galaxies. 

At the Centre for Astrophysics and Supercomputing (CAS), we are leading the SAGES Legacy Unifying Globulars and Galaxies (SLUGGS) Survey - a wide-field chemo-dynamical survey of early-type galaxies. It capitalises on the unmatched observing power of the Subaru/Suprime-Cam imager and the Keck/DEIMOS spectrograph, combined with state-of-the-art simulations to interpret the observations in a cosmological context. Spectroscopy of the near-infrared calcium triplet provides kinematic and metallicity information for stars (to ~3 effective radii) and globular clusters (to ~10 effective radii) in two dimensions around the survey galaxies.

The science goals are to map out halo substructure, mass, angular momentum, metallicity gradients, orbital structure and the distribution of dark matter. These fundamental characteristics provide important clues about the assembly histories of galaxies. The survey is a key project of the Study of the Astrophysics of Globular Clusters in Extragalactic Systems (SAGES) network and is supported by the Australian Research Council and National Science Foundation.

At CAS, we are also focused on understanding the complicated internal dynamical evolution of star clusters through simulations performed on the Swinburne supercomputer. The old and massive globular clusters can contain a million stars or more. They represent dense stellar environments which on one hand can produce stellar exotica, e.g. mergers of black holes, through close interactions between stars, but these same interactions can also modify the lifetime and characteristics of the clusters themselves. We aim to investigate and quantify such effects using sophisticated N-body software that models stellar, binary and cluster evolution in parallel.