My research interests have focused on two main subjects. I give a brief description of each in what follows.

I. Galaxy Formation and Evolution:

There are competing galaxy formation scenarios.  For example, in the classical monolithic collapse scenario galaxies form early via the gravitational collapse of large gas clouds. In contrast, under the hierarchical formation scenario galaxies today are the result of multiple merging of subclumps over the age of the universe. While the hierarchical scenario tends to be favored in recent years due, mainly, to the success of the λCDM model, the fine details of galaxy formation are still a matter of debate. In recent years, a hybrid of the above two classical scenarios has gained popularity. This scenario is usually refered to as "two-phase" galaxy formation scenario. Evidence for this latter scenario is slowly accumulating, explaining its increasing popularity.

By measuring metallicities of the unresolved stellar populations of galaxies I hope to help disentangling between these two scenarios by comparing with their respective predictions. My research is four-fold:
1) I look at the globular clusters around large elliptical galaxies as probes of early star formation;
2) I study the metal composition of the galaxy stars at large galactocentric radii where the predictions from various galaxy formation models differ most;
3) I use the kinematic information extracted from the spectra of member stars of relatively nearby galaxies (within ~30 Mpc), their globular clusters, planetary nebulae and HII regions in order to look for signs of recent mergers, thereby helping to understand and reconstruct their assembly history;
4) Using spectra from the GAlaxy and Mass Assembly (GAMA) survey, I study the metal enrichment of the Universe.

Above: Subaru Suprime-Cam image of the 'ordinary' elliptical galaxy NGC 4494 with some background galaxies, foreground stars and a whole heap of globular clusters appearing as small points of light. (Image credit: L. Spitler)

II. Cosmological Voids:

Large redshift galaxy surveys allow astronomers to map out the three-dimensional distribution of galaxies in our Universe. In the 1970's and 1980's it was discovered that instead of being uniformly distributed in space, galaxies tend to regroup in clusters, filaments that define the boundary of large void regions. Cosmological voids are large region of space which are almost completely devoid of luminous matter (i.e., galaxies).

A void finding algorithm that objectively identifies and quantifies the salient properties of cosmological voids has been implemented (see Foster & Nelson 2009). Several algorithms already exist but a conventional and coherent definition for voids does not yet exist. The Aspen-Amsterdam void finder comparison project (Colberg et al. 2008) compares and contrasts the results from different algorithms on the same dataset.  Our algorithm was used to identify voids in the Sloan Digital Sky Survey (SDSS) and in a mock semi-analytic catalog by Croton et al. (2006). The website  for this project can be found here.

Above: A slice of our Universe as revealed by the SDSS. We are located at the centre and each point represents a galaxy. Galaxies are not randomly distributed but tend to cluster together leaving behind large voids called cosmological voids. (Image credit: M. Blanton et le Sloan Digital Sky Survey.)

Colberg et al. 2008, MNRAS, 387, 933
Croton et al., 2006, MNRAS, 365, 11
Foster & Nelson, 2009, ApJ, 699, 1252