The Shapley Supercluster
The Shapley supercluster core (SSC) represents an ideal target for the investigation of the role played by environment in the transformation of galaxies, and has been investigated by numerous authors since its discovery (Shapley 1930). It is one of the richest supercluster in the nearby universe, consisting of as many as 25 Abell clusters in the redshift range 0.035 < z < 0.055. Extensive redshift surveys (Bardelli et al. 2000; Quintana, Carrasco & Reisenegger 2000; Drinkwater et al. 2004) indicate that these clusters are embedded in two sheets extending over a ~ 10 × 20 sqdeg region of sky (~35 × 70 h70-2 Mpc2), and that as many as half the total galaxies in the supercluster are from the intercluster regions. The Shapley core (see figure) is constituted by three Abell clusters: A 3558 (z = 0.048, Melnick & Quintana 1981; Metcalfe, Godwin & Spencer 1987; Abell richness R = 4, Abell, Corwin & Olowin 1989), A 3562 (z = 0.049, Struble & Rood 1999, R = 2, Abell et al. 1989) and A 3556 (z = 0.0479, Struble & Rood 1999, R = 0, Abell et al. 1989) and two poor clusters SC 1327-312 and SC 1329-313. Dynamical analysis indicates that at least a region of radius 11 h70-1 Mpc centred on the central cluster A 3558, and possibly the entire supercluster, is past turnaround and is collapsing (Reisenegger et al. 2000), while the core complex itself is in the final stages of collapse, with infalling velocities reaching ~2000 km/s.
A major study of the dynamical properties of the
supercluster core was performed by Bardelli, Zucca & Baldi (2001,
and reference therein). They showed that the supercluster core has a complex,
highly elongated structure, and identified 21 significant three-dimensional
subclumps, including eight in the A 3558 cluster alone.