2004ApJ...607L...1G

We present spectroscopic confirmation of the Cl 1604 supercluster at z∼0.9. The supercluster was originally detected as two individual clusters, Cl 1604+4304 at z=0.90 and Cl 1604+4321 at z=0.92, which are closely separated in both redshift and sky position. Subsequent imaging revealed a complex of red galaxies bridging the two clusters, suggesting that the region contained a large-scale structure. We have carried out extensive multiobject spectroscopy, which, combined with previous measurements, provides ∼600 redshifts in this area, including 230 confirmed supercluster members. We detect two additional clusters that are part of this structure, Cl 1604+4314 at z=0.87 and Cl 1604+4316 at z=0.94. All four have properties typical of local clusters, with line-of-sight velocity dispersions between 489 and 962 km/s. The structure is significantly extended in redshift space, which, if interpreted as a true elongation in real space, implies a depth of 93 h^–1₇₀Mpc. We examine the spatial and redshift distribution of the supercluster members.