Andrew Butler

PhD Student

Swinburne University of Technology (Melbourne, Australia)

Description of PhD Thesis:

It has been known for some time that galaxy evolution is a function of environment. The densest and most interesting of environments are galaxy clusters, which are among the most massive gravitationally bound structures in the universe. It is thought that the most massive and luminous galaxies in the universe, which are early type ellipticals and mostly reside in the dense centers of clusters, formed relatively early in the history of the universe via the process of hierarchical merging (i.e. galaxy collisions). It has also been known for some time that the fraction of blue late type galaxies in clusters, which mostly reside in the less dense outer regions, increases with higher redshift (known as the Butcher Oemler effect). This means that the star formation in galaxies falling to the center of clusters has been suppressed somehow over the history of the universe. For my thesis I am investigating the mechanisms behind this phenomenon using optical data of galaxies in clusters in a wide range of redshifts to determine their evolution, both spectroscopically and morphologically, as a function of environment and redshift. Since radio jets that emanate from the elliptical galaxies and heat the interstellar medium, thus preventing star formation, are becoming increasingly evident, I also use radio data to investigate the connection between radio emission and star formation suppression. My studies should allow insight into the link (or lack thereof) between the morphology-density relation, the Butcher Oemler effect, the processes responsible for the termination of star formation in galaxies, and the relative importance of major merging events between clusters.

Galaxy Cluster MS1358+62

Caption: This is an HST WFPC2 mosaic of the central regions of galaxy cluster MS1358+62, which is at a redshift of z=0.328. We have proposed to observe the spectra of the blue galaxies in order to measure their mass (from their rotation curves), which should allow us to determine whether they are the progenitors of S0 galaxies or of the dwarf galaxy population in low-redshift rich clusters.

See my official Swinburne page