Discovery of extreme examples of superclustering in Aquarius

The results of spectroscopic observations of 46 R greater than or equal to 1 clusters of galaxies from the Abell and Abell, Corwin, & Olowin (hereafte r AGO) catalogs are presented. The observations were conducted at the ESO 3 .6 m telescope with the Meudon-ESO Fibre Optics Spectrograph (MEFOS) multip le-fiber spectrograph. Thirty-nine of the clusters lie in a 10 degrees x 45 degrees strip of sky that contains two supercluster candidates (in Aquariu s and Eridanus). These candidates were identified by a percolation analysis of the Abell and ACO catalogs, using estimated redshifts for clusters that had not yet been measured. With our measurements and redshifts from the li terature, the target strip is now 85% complete in redshift measurements for R greater than or equal to 1 ACO clusters with m(10) less than or equal to 18.3. Seven other clusters were observed in a supercluster candidate in th e Grus-Indus region. Seven hundred thirty-seven galaxy redshifts were obtai ned in these 46 cluster fields. We find that one of the supercluster candid ates is a collection of 14 R greater than or equal to 1 ACO/Abell clusters with a spatial number density that is 20 times the average spatial density for rich ACO clusters. This overdensity has a maximum extent of similar to 110 h(-1) Mpc, making it the longest supercluster composed only of R greate r than or equal to 1 clusters to be identified to date. This filament of cl usters runs within 6 degrees of the line of sight in the Aquarius region, a nd, on its high-z end, four R = 0 ACO clusters (three of which are R = 1 in the Abell catalog) appear to bridge gaps to other clusters, extending the structure to similar to 150 h(-1) Mpc. Our analysis also reveals that anoth er supercluster, consisting of eight rich clusters with an extent of simila r to 75 h(-1) Mpc, runs roughly perpendicular to Aquarius near its low-reds hift end. Both of these superclusters are remarkably filamentary. Fitting e llipsoids to all N greater than or equal to 5 clumps of clusters (at b = 25 h-l Mpc) in the measured-z Abell/ACO R greater than or equal to 1 clusters sample, we found two other superclusters with axis ratios greater than or equal to 3 (long-to-midlength axis). The frequency of such filaments (simil ar to 20%) was nearly identical with that found among "superclusters" in Mo nte Carlo simulations of random and random-clumped cluster samples, however , so the Abell/ACO clusters have no particular tendency toward filamentatio n. The Aquarius and Aquarius-Cetus superclusters, in this one region of the sky, have axis ratios of 4.3 and 3.0, respectively. The Aquarius filament also contains a "knot" of six R greater than or equal to 1 clusters at z si milar to 0.11, with five of the clusters close enough together to represent an apparent overdensity of 150 (n) over bar. There are three other R great er than or equal to 1 cluster density enhancements similar to this knot at lower redshifts: Corona Borealis, the Shapley concentration, and another gr ouping of seven clusters in Microscopium. Al four of these dense superclust ers appear near the point of breaking away from the Hubble flow, and some m ay now be in collapse, but there is little indication of any being virializ ed. With four such objects, studies of them as a class may now lead to much greater insight into large-scale processes.