Discovery of a High-Redshift (z=0.96) Cluster of Galaxies Using a FIRST Survey Wide-Angle-Tailed Radio Source

Using a combination of near-infrared and optical photometry, along with multiobject spectroscopy, we have confirmed the existence of a high-redshift cluster of galaxies at z=0.96. The cluster was found using a wide-angle-tailed radio source selected from the VLA FIRST survey as a cluster signpost. These types of radio sources are often found in clusters and are thought to attain their C-shaped morphologies from the relative motion between the radio source host galaxy and the intracluster medium. We present optical/near-infrared color-magnitude diagrams that show a concentration of cluster galaxies in color space. We also include spectroscopic results obtained from the Keck II Low Resolution Imaging Spectrometer. Ten galaxies are confirmed at the cluster redshift, with a line-of-sight velocity dispersion of σ_∥=530⁺¹⁹⁰_-90 km s^-1, typical of an Abell richness class 0 cluster. Using data from the ROSAT public archive, we limit the X-ray luminosity for the cluster to L_X,bol<~3×10⁴⁴ ergs s^-1, consistent with the value expected from the L_X-σ relation.

Based in part on observations obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.