AN IR-SELECTED GALAXY CLUSTER AT Z=1.27

We report the discovery of a galaxy cluster at z=1.27. CIG J0848+4453 was found in a near-IR field survey as a high density region of object s with very red J-K colors. Optical spectroscopy of a limited number o f 24 less than or similar to R less than or similar to 25 objects in t he area shows that 6 galaxies within a 90 arcsec (0.49h(100)(-1), Mpc, q(0) = 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 s pectral energy distribution of a passively-evolving elliptical galaxy formed at high redshift, An additional 2 galaxies located similar to 2 arcmin from the cluster center are also at z = 1.27. Using all 8 of t hese spectroscopic members, we estimate the velocity dispersion sigma= 700+/-180 km s(-1), which in similar to that of Abell richness class R = 1 clusters in the present epoch. A deep ROSAT/PSPC observation dete cts X-ray emission at the 4.5 sigma level coincident with the nominal cluster center. Assuming that the X-ray flux is emitted by hot gas tra pped in rbe potential well of a collapsed system (no AGN are known to exist in the area), the resulting X-ray luminosity in the rest frame 0 .1-2.4 keV band of L-x = 1.5 X 10(44) ergs s(-1) suggests the presence of a moderately massive system, CIG J0848+4453 is the highest redshif t cluster found in a held survey. (C) 1997 American Astronomical Socie ty. [S0004-6256(97)02112-2].