curriculum vitae link:  Greg's CV


I am a Giacconi Fellow at the Space Telescope Science Institute. My research focus is the formation and evolution of galaxies, which I study by performing numerical simulations on supercomputers such as the Odyssey, Gordon, and Pleiades clusters, as well as by analyzing data taken with instruments aboard the Hubble Space Telescope, at the W.M. Keck Observatory, and others. I am actively involved in predicting what the James Webb Space Telescope might teach us about the origins of galaxy structure.

Visual demos of some of my recent work are here and here (, and an overview of my work can be found here.


In October 2016, I submitted a paper addressing the unexpected behavior of distant galaxy pair statistics:

In July 2015 I gave a talk at Mocking the Universe, an STScI Mini-Workshop. Videos are online here. My talk, Observing Galaxy Assembly in Simulations, is available here.

In October 2014 I gave a talk in the STScI Public Lecture Series: Studying Virtual Universes with Supercomputer Simulations, embedded link below:

As a postdoc at STScI, I create and analyze synthetic data from simulations of galaxy formation, treating them as if they were observed by the Hubble Space Telescope and in the future the James Webb Space Telescope. A recent paper analyzing the shapes of distant galaxies in very detailed simulations was posted in September 2014: arXiv:astro-ph/1409.1583

I am also involved in a collaboration (The Illustris Project) to create and analyze large-scale simulations of galaxy formation. I summarized my perspective on this project in a short post for STScI's research blog An Eye on the Universe: Observing Galaxy Formation in Simulations. Part of my contribution was to generate a side-by-side comparison of the Illustris Simulation with the Hubble Space Telescope Ultra Deep Field (XDF data release):

On the left is a 2.8 by 2.8 arcminute image of the UDF at three wavelengths, and on the right is an image of the same volume from a random sight-line through the Illustris Simulation. The mock image is in the same units as the real one, and was processed to closely mimic the effects of telescope resolution and noise. Broadly speaking, we find a mix of galaxy shapes and colors reminiscient of the real universe. Only recently have hydrodynamic simulations of galaxy formation reached the size and accuracy required to make such a direct comparison.