The Horologium-Reticulum supercluster of galaxies

Redshifts, morphological classifications, orientations and ellipticities are presented for 129 galaxies within a 6° × 6° region in Horologium–Reticulum centred on |3^ h27^ m|⁠, –53°. 5. The survey shows that the prominent clusters in the region form a supercluster with a mean redshift around 18 000 km s−1. The region is dominated by two very rich clusters Cl 0329 – 527 (Klemola 8) and Cl 0342 – 538 (Calan 0340 – 538) which are separated by a projected distance of |8 h^-1 Mpc (h = H₀/100 km s^-1 Mpc^-1) |⁠. The line-of-sight velocity dispersion of these clusters is close to 1000 km s−1 whereas those of the less rich aggregates lie in the range 300 to 400 km s−1. Redshifts indicate that there is a bridge of galaxies connecting Cl 0342 – 538 to the prominent aggregate Cl 0326 – 537 which lies to the south-west of Cl 0329 – 527. The galaxy position angles are preferentially aligned along the bridge. A simple two-particle model, assuming masses derived from the application of the virial theorem to each of the two very rich clusters, suggests that they are approaching each other and will collide within 0. 5 of a Hubble time. The properties of the individual supercluster components are discussed. A newly discovered rich background cluster, Cl 0328 – 558, has a velocity dispersion close to 900 km s−1. Several foreground groups have been discovered; the most prominent covers most of our survey region, has a redshift of 13 700 km s−1 and a velocity dispersion of only 210 km s−1. Several regions appear to be devoid of galaxies, the largest of which has a redshift depth of 25 h−1 Mpc. Most galaxies are associated with some cluster or group, a pattern similar to that found in other surveys.