D. Emerson

Three-Dimensional Structure in the Indus Supercluster

Redshifts of large numbers of galaxies can be obtained to an accuracy of ±0.01 in Z by measurement of their spectra on UK Schmidt Telescope objective-prism plates using the COSMOS plate-scanning machine. 2294 redshifts have been measured in a 4.7 × 5.2 deg area of the sky which includes part of the Indus supercluster. The redshifts enable the three-dimensional distribution of the galaxies within the supercluster to be investigated, and a subset of this data is presented here. A 6.8 h−1 bridge of galaxies connecting the rich clusters 2151–5805 and 2143–5732 is revealed (h = Ho/100 km sec−1 Mpc−1). A concentration of galaxies, apparently coincident with 2151–5805 on the sky, is found to lie in the background at a higher redshift, illustrating how the knowledge of redshifts can resolve structure in three dimensions. Much faster and more objective automatic methods of determining the redshifts are currently being developed.