An X-ray Selected Galaxy Cluster at Z = 1.26

We report the discovery of an X-ray luminous galaxy cluster at z = 1.26. RXJ0848.9+4452 was selected as an X-ray cluster candidate in the ROSAT Deep Cluster Survey, on the basis of its spatial extent. Deep optical and near-IR imaging have revealed a galaxy overdensity around the peak of the X-ray Based in part on observations obtained at the W.M. Keck Observatory Based in part on observations obtained at the Kitt Peak National Observatory Physics Department, University of California at Davis, Davis, CA 95616. Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.