Discovery of Extreme Examples of Superclustering in Aquarius

The results of spectroscopic observations of 46 R " 1 clusters of galaxies from the Abell and Abell, Corwin, & Olowin (hereafter ACO) catalogs are presented. The observations were conducted at the ESO 3.6 m telescope with the Meudon-ESO Fibre Optics Spectrograph (MEFOS) multiple-—ber spectrograph. Thirty-nine of the clusters lie in a 10i ) 45i strip of sky that contains two supercluster candidates (in Aquarius and Eridanus). These candidates were identi—ed by a percolation analysis of the Abell and ACO catalogs, using estimated redshifts for clusters that had not yet been measured. With our measure- ments and redshifts from the literature, the target strip is now 85% complete in redshift measurements for R " 1 ACO clusters with Seven other clusters were observed in a supercluster candidate m 10 " 18.3. in the Grus-Indus region. Seven hundred thirty-seven galaxy redshifts were obtained in these 46 cluster —elds. We —nd that one of the supercluster candidates is a collection of 14 R " 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 D110 h~1 Mpc, making it the longest supercluster composed only of R " 1 clusters to be identi—ed to date. This —lament of clusters runs within 6i of the line of sight in the Aquarius region, and, on its high-z end, four R \ 0 ACO clusters (three of which are R \ 1i n the Abell catalog) appear to bridge gaps to other clusters, extending the structure to D150 h~1 Mpc. Our analysis also reveals that another supercluster, consisting of eight rich clusters with an extent of D75 h~1 Mpc, runs roughly perpendicular to Aquarius near its low-redshift end. Both of these superclusters are remarkably —lamentary. Fitting ellipsoids to all N " 5 clumps of clusters (at b \ 25 h~1 Mpc) in the measured-z Abell/ACO R " 1 clusters sample, we found two other superclusters with axis ratios "3 (long-to-midlength axis). The frequency of such —laments (D20%) was nearly identical with that found among ii superclusters ˇˇ in Monte Carlo simulations of random and random-clumped cluster samples, however, so the Abell/ACO clusters have no particular tendency toward —lamentation. The Aquarius and Aquarius-Cetus superclusters, in this one region of the sky, have axis ratios of 4.3 and 3.0, respec- tively. The Aquarius —lament also contains a ii knot ˇˇ of six R " 1 clusters at z D 0.11, with —ve of the clusters close enough together to represent an apparent overdensity of 150 There are three other n6 . R " 1 cluster density enhancements similar to this knot at lower redshifts: Corona Borealis, the Shapley concentration, and another grouping of seven clusters in Microscopium. All four of these dense super- clusters appear near the point of breaking away from the Hubble —ow, and some may now be in col- lapse, but there is little indication of any being virialized. With four such objects, studies of them as a class may now lead to much greater insight into large-scale processes. Subject headings: galaxies: clusters: generalgalaxies: distances and redshifts