Key points are not available for this paper at this time.
We report the discovery of a galaxy cluster at z=1. 27. ClG J0848+4453 was found in a near-IR field survey as a high density region of objects with very red J-K colors. Optical spectroscopy of a limited number of 24 < R < 25 objects in the area shows that 6 galaxies within a 90 arcsec (0. 49/h Mpc, qO = 0. 1) diameter region lie at z=1. 273 +/- 0. 002. Most of these 6 member galaxies have broad-band colors consistent with the expected spectral energy distribution of a passively-evolving elliptical galaxy formed at high redshift. An additional 2 galaxies located ~2 arcmin from the cluster center are also at z=1. 27. Using all 8 of these spectroscopic members, we estimate the velocity dispersion is 700 +/- 180 km/s, similar to that of Abell R=1 clusters in the present epoch. A deep Rosat PSPC observation detects X-ray emission at the 5 sigma level coincident with the nominal cluster center. Assuming that the X-ray flux is emitted by hot gas trapped in the potential well of a collapsed system (no AGN is known to exist in the area), the resulting X-ray luminosity in the rest frame 0. 1-2. 4 keV band of Lₓ = 1. 5 x 10⁴4 ergs/s suggests the presence of a moderately large mass. ClG J0848+4453 is the highest redshift cluster found without targetting a central active galaxy.
Stanford et al. (Mon,) studied this question.