The evolution of galaxy in X-ray galaxy groups and clusters

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Clusters of galaxies are equivalent to the towns and cities in which individual galaxies live and grow. My research is based upon finding new galaxy clusters and studying the galaxies they contain. I achieve this using space borne X-ray observatories - named "Newton" and "Chandra" - which capture images of the hot clouds of gas associated with galaxy clusters. The heat contained in the X-ray gas is a clue to how massive the galaxy cluster is - like a mass "label" - it is similar to reading the label on a sweater and working out how big it will be. I then use a wide variety of telescopes - in the optical and infrared, from ground and space - to study the "life history" of each galaxy in each cluster. What results is a huge map of changing galaxy properties (big-small, old-young) each attached to a galaxy cluster, and each cluster with a label telling us how massive it is. To achieve this, my graduate students and I are working with a large, international team of astronomers; just like the national census tells us abouts trends in our nation, this "galaxy census" tells us about how the universe came to look like it does today.