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I've summarized a few of my main research topics below, along with some of the associated web sites and publications. For those interested, you can also see a full List of Publications.
Virgo Cluster
Fornax Cluster
I am a member of the teams for the ACS Virgo Cluster Survey, the ACS Fornax Cluster Survey, and the Coma Cluster Treasury Survey.  Using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, these surveys have imaged 100 early-type galaxies in the Virgo Cluster and 43 early-type galaxies in the Fornax Cluster, and portions of the Coma Cluster.  

Much of my current work focuses on the Next Generation Virgo Survey (NGVS), a Large Program approved for CFHT/Megacam to obtain deep, ugriz images of most of the Virgo galaxy cluster (100 deg2).  I and my collaborators are using these images to study galaxies, globular cluster systems, diffuse star clusters, stellar nuclei, and Galactic structure.
NGC 5694 Globular clusters are collections of tens to hundreds of thousands of stars all orbiting each other due to their mutual gravity.  Globular clusters contain some of the oldest stars in the universe, and are remnants of vigorous periods of past star formation.  Most galaxies above a certain mass seem to have a system of globular clusters, making them useful tools for understanding the early formation of galaxies.
Selected Publications Popular Media
Planetary Nebula Abell 39 (credit: Jacoby/NOAO) Planetary nebulae are low and intermediate mass stars that are shedding their outer envelopes and becoming white dwarfs.  During this brief phase, the hot central stars ionize and heat the surrounding nebula, causing it to glow with characteristic emission lines.  These lines make them easy to detect even in distant galaxies.  I use these lines to measure the velocities of extragalactic planetary nebulae, and from the velocities I can measure total mass and dark matter content in nearby galaxies.
NGC 5128 (Cen A) Galaxy mergers are very important for assembling the galaxies we see today.  I have been studying the nearby post-merger galaxy NGC 5128 (Centaurus A) for clues on how it got to be such a mess.  Although big mergers are important, small ones are too, and we found a young stellar stream in this galaxy that may be the remnant of a gaseous dwarf galaxy that fell in has been tidally disrupted.
Publication Popular Media

Looking west from Cerro Tololo
Eric Peng's Web Abode