The Most Distant X-Ray Clusters

In this program we have used ROSAT (Roentgen Satellite Mission) to observe X-ray emission around several high redshift radio galaxies in a search for extended, hot plasma which may indicate the presence of a rich galaxy cluster. When this program was begun, massive, X-ray emitting galaxy clusters were known to exist out to to z=0.8, but no more distant examples had been identified. However, we had identified several apparently rich clusters around 3CR radio galaxies at z greater than 0.8, and hoped to use ROSAT to confirm the nature of these structures as massive, virialized clusters. We have written up our results and submitted them as a paper to the Astrophysical Journal. This paper has been refereed and requires some significant revisions to accommodate the referees comments. We are in the process of doing this, adding some additional analysis as well. We will resubmit the paper early in 2000, and hopefully will meet with the referee's approval. We are including three copies of the submitted paper here, although it has not yet been accepted for publication.