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.

The surface density of R,18.5 galaxies in the SSC obtained by using data of the SuperCosmos Sky Survey (Hambly et al. 2001). Red rectangles indicate the B- and R-band images of ACCESS.

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.
The X-ray observations show that the supercluster has a flattened and elongated morphology where clusters outside the dense core are preferentially located in hot gas filaments (Bardelli et al. 1996; Kull & Bohringer 1999; De Filippis, Schindler & Erben 2005). Moreover, Finoguenov et al. (2004) showed a strong interaction between the cluster A 3562 and the nearby group SC 1329-313 with an associated radio emission having young age (Venturi et al. 2000, 2003).
However, since this is one of the weakest radio holoes found, Venturi et al. (2003) suggested that this halo is connected with the head-on radio galaxy of A 3562. Bardelli et al. (2001) suggested that the A 3558 complex is undergoing a strong dynamical evolution through major merging seen just after the first core-core encounter, and so the merging event has already been able to induce modifications in the galaxy properties. Recently, Miller (2005), with a radio survey of a 7 sqdeg region of SSC, found a dramatic increase in the probability for galaxies in the vicinity of A 3562 and SC 1329-313 to be associated with radio emission. He interpreted this fact as a young starburst related to the recent merger of SC 1329-313 with A3562.

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