A low mass cluster of extremely red galaxies at z=1.10 in the GOODS Southern Field

We have studied the spatial clustering of high redshift (z > 1) extremely red objects (EROs) as a function of photometric redshift in the GOODS Southern Field using public data. A remarkable overdensity of extremely red galaxies (I - K-s > 4) is found at an average photometric redshift z(phot) = 1.10. Nine objects (six are EROs) within 50 arcsec of the brightest infrared galaxy in this overdensity present spectroscopic redshifts in the range 1.094 < z(spec) < 1.101 with a line-of-sight velocity dispersion of sigma(v) = 433(-74)(+152) km s(-1) typical of an Abell richness class R = 0 cluster. Other potential members of this cluster, designated as GCL J0332.2-2752, have been identified using photometric redshifts and the galaxy density profile studied as a function of radius. The mass of the cluster is preliminary estimated at M-cl similar to 5-7 x 10(13) M-circle dot. Using available Chandra data, we limit the rest-frame X-ray luminosity of the cluster to less than L-X = 7.3 x 0(42) erg s(-1) (0.5-2.0 keV). This low-mass, low L-X cluster at z > 1 shows the potential of EROs to trace clusters of galaxies at high redshift.