An X-Ray Cluster at Redshift 2.156?

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Abstract
We present X-ray observations of the narrow-line radio galaxy 1138-262 at z=2.156 with the High Resolution Imager (HRI) on ROSAT. Observations at other wave bands, and in particular extremely high values of Faraday rotation of the polarized radio emission, suggest that the 1138-262 radio source is in a dense environment, perhaps a hot, cluster-type atmosphere. We detect X-ray emission from the vicinity of 1138-262, and we discuss possible origins for this emission. The X-ray, optical, and radio data all favor thermal emission from a hot cluster atmosphere as the mechanism responsible for the X-rays, although we cannot rule out a contribution from the active nucleus. If this interpretation is correct, then 1138-262 becomes the most distant, by far, of known X-ray-emitting clusters. The X-ray luminosity for 1138-262 is 6.7±1.3×1044 ergs s-1 for emitted energies between 2 and 10 keV.
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