I spend most of my time trying to understand how galaxies form and constructing computer simulations of their properties. Much of my research makes use of a technique rather unfortunately known as 'semi-analytic' modelling. A semi-analytic model is simply a set of recipes and approximations that keep track of how much mass has collapsed and formed gravitationally bound objects over time (represented via a 'merger tree' like the one pictured to the right), and how much gas has cooled and formed stars, how much energy these stars have returned to the interstellar medium, etc. My collaborators and I are currently working on implementing these recipes within merger trees extracted from high-resolution N-body simulations, which provide information about how dark matter halos cluster with one another, and also about the internal properties of those halos, such as their mass profiles and their internal angular momentum. We will use this additional information to predict the properties of the internal structure of galaxies (such as their size or scale length) and how they cluster in space.
See this page for a short list of background literature on this work.
I am actively involved in a number of observational projects that are surveying the Universe in many wavelengths across the electromagnetic spectrum. These projects make use of telescopes on the ground (like Keck and the VLT) and in space (like Chandra, GALEX, HST, and Spitzer). Some of these projects include:
- the Great Observatories Origins Deep Survey (GOODS)
- Galaxy Evolution from Morphology & SEDs (GEMS)
- the Ultra Deep Field (UDF)
- the DEEP redshift survey and Extended Groth Strip (EGS) survey project
- why did the star formation rate decline from z~1 to the present, and what kind of galaxies contribute to the global star formation budget as a function of time?
- how did the merger rate evolve over time, and what was the relative role of mergers vs. accretion in the assembly of galaxies?
- how can we best extract physical galaxy properties like size, mass, and specific star formation rate from the directly observable quantities derived from images or spectra?
I am interested in the nature of the first stars, galaxies, and AGN in the Universe, and related questions such as:
- when did the first stars and black holes form?
- how did they affect their environment?
- how were future generations of stars impacted by these side effects?
Observations from the UV to the radio have revealed that reprocessing of light by dust has an important impact on the appearance of galaxies, especially at high redshift. Half to two-thirds of the integrated light that we see today was reprocessed by dust. My collaborators and I are working on improving the modelling of dust in cosmological simulations of galaxy formation, using detailed simulations with radiative transfer, and on comparing the model predictions with multi-wavelength data from the UV to the far IR from GALEX, HST, Spitzer, etc.
See this page for links to papers on the dust and radiative transfer simulations.