Research Interests
My primary focus of research is in the field of observational cosmology, with an emphasis on using gravitational lensing to study massive structures such as clusters of galaxies. Among the goals of my research are: Determining the nature of dark matter and dark energy, measuring the structural evolution of  clusters of galaxies and related objects, measuring cosmological parameters, and determining the redshifts of galaxies too faint to measure spectroscopically. I also do research on the evolution of the galaxy populations in clusters as well as the high redshift galaxies used as the sources of the gravitational lensing studies.
 
Current Research Projects:
  1. Merging Clusters of Galaxies -  using optical, infrared, and X-ray images and spectroscopy to study interacting clusters of galaxies. We perform gravitational lensing measurements on the optical  images to measure the location and amount of mass in the clusters.  By comparing this with the X-ray images, which show where 90% of the baryons in the clusters are located (the remaining 10% are in the galaxies), we have shown that irrespective of how the gravitational force law behaves on Megaparsec scales, the majority of the mass in these systems must be some type of dark matter, and have placed constraints on the self-interaction cross-section of the dark matter particles. We are also investigating how much shock heating of the X-ray plasma occurs during the collision, which will determine how large of errors can exist in cluster mass measurements from X-ray observations. We are using the spectroscopy to measure the kinematics of the cluster mergers and to determine how much star formation is induced by these types of major mergers. We have published several papers over the past year on one cluster in this study, 1E0657-556 (also called the “Bullet Cluster"), and have received Chandra and HST time to study more merging cluster systems.  
  2. European Distant Cluster Survey (EDisCS) - a sample of 20 high-redshift (0.4 < z < 1.0) clusters of galaxies with optical and infrared imaging and spectroscopy. I am the lead investigator on the imaging side of the program. Some of the primary goals of the survey include measuring the structural evolution of clusters with redshift and measuring the evolution of the cluster galaxies both in terms of global properties and for the bulge and disk components seperately.  We are also using these galaxy clusters as gravitational telescopes to look for populations of high redshift galaxies too faint to detect otherwise.
  3. LSST - The Large Synoptic Survey Telescope is a proposed 8-meter ground-based telescope capable of imaging the entire available sky every 3 nights.  It is being designed to detect near-Earth asteroids, supernovae, and to measure the evolution of structures in the university gravitational lensing.  I am a member of the weak lensing science working group.
  4. DESTiny - The Dark Energy Space Telescope is a proposed space-based telescope to measure the evolution of dark energy (the most massive component of our universe, for which we have very little information as to what it is).  This is done by both detecting several thousand distant supernovae and making a map of how the dark matter structures have changed over the history of the universe using gravitational lensing.  DESTiny is one of the three finalists for the Joint Dark Energy Mission.