Superclustering at redshift z=0.54

We present strong evidence for the existence of a supercluster at a redshift of z = 0.54 in the direction of Selected Area 68 (SA68). From the distribution of galaxies with spectroscopic redshifts, we find that there is a large over density of galaxies (a factor of 4 over the number expected in an unclustered universe) within the redshift range 0.530 < z < 0.555. By considering the spatial distribution of galaxies within this redshift range (using spectroscopic and photometric redshifts), we show that the galaxies in SA68 form a linear structure passing from the Southwest of the survey field through to the Northeast (with a position angle of approximately 35 degrees east of north). This position angle is coincident with the positions of the X-ray clusters CL 0016+16, RX J0018.3+1618 and a new X-ray cluster, RX J0018.8+1602, centered near the radio source 54W084. All three of these sources are at a redshift of z similar to 0.54 and have position angles, derived from their X-ray photon distributions, consistent with that measured for the supercluster. Assuming a redshift of 0.54 for the distribution of galaxies and a FWHM dispersion in redshift of 0.020, this represents a coherent structure with a radial extent of 31 h(-1) Mpc, transverse dimension of 12 h(-1) Mpc, and a thickness of similar to 4 h(-1) Mpc. The detection of this possible supercluster demonstrates the power of using X-ray observations, combined with multicolor observations, to map the large-scale distribution of galaxies at intermediate redshifts.