A GUIDED TOUR OF THE SHAPLEY CONCENTRATION SUPERCLUSTER:

    The Large Scale Structure

    The distribution of clusters inside the Shapley Concentration is quite well studied; on the contrary, little is known about the distribution and the overdensity of intercluster galaxies. For this reason we performed a redshift survey of galaxies which are outside the clusters and the obvious bi--dimensional overdensities in this region, in order to derive the distribution and the overdensity of ``field" objects. These data have been added to our surveys covering the cluster complexes (Bardelli et al. 1994, 1998a, 2000b), resulting in a total redshift sample of about 2000 radial velocities. In Figure 1 we show our sampling strategy: big and small circles correspond to the field of view of the MEFOS and OPTOPUS multifiber spectrographs (at the 3.6m ESO telescope), respectively. In Figure 2 we show the wedge diagram of our sample. It is clear the presence of the two cluster complexes dominated by A3558 (on the left) and by A3528 (on the right). These two structures appear to be connected by a bridge of galaxies, resembling the Coma-A1367 system, the central part of the Great Wall. The scale of this system is $\sim 23$ \hmpc and it is comparable to that of Coma-A1367 ($\sim 21$ \hmpc). Note the presence of two voids at $\sim 20000$ km/s and $\sim 30000$ km/s in the easternmost half of the wedge, labelled as V1 and V2 respectively. Other two voids (V3 and V4) are visible in the westernmost part of the plot: in particular, void V3 appears to be delimited by two elongated features (S300a and S300b) which appear to ``converge" in a single feature at right ascension $\sim 13^h$ (S300c). We refer to this structure with the name S300: as shown below, the overdensity corresponding to this excess is remarkably high. Our main results are the following (Bardelli et al. 2000a):

    -- The average velocity of the observed intercluster galaxies in the Shapley Concentration appears to be a function of the ($\alpha$, $\delta$) position, and can be fitted by a plane in the three--dimensional space ($\alpha$, $\delta$, $v$): the distribution of the galaxy distances around the best fit plane is described by a Gaussian with $\sigma =3.8$ \hmpc.

    -- Using the 1440 galaxies of our sample in the magnitude range $17 - 18.8$, we reconstructed the density profile in the central part of the Shapley Concetration and we detected another significant overdensity at $\sim 30000$ km/s.

    -- We estimate the total overdensity in galaxies, the mass and the dynamical state of these structures, discussing the effect of considering a bias between the galaxy distribution and the underlying matter. The estimated total overdensity in galaxies of these two structures is $\displaystyle{ N \over \bar{N}}\sim 5.2$ on scale of $15.5$ \hmpc for the Shapley Concentration and $\displaystyle{ N \over \bar{N}} \sim 2.9$ on scale of $24.8$ \hmpc for S300. If light traces the mass distribution, the corresponding masses are $2.3\times 10^{16}$ $\Omega$ h$^{-1}$ M$_{\odot}$ and $5.1\times 10^{16}$ $\Omega$ h$^{-1}$ M$_{\odot}$ for Shapley Concentration and S300, respectively.

    The dynamical analysis reveals that, if light traces mass and $\Omega=1$, the Shapley Concentration already reached its turnaround radius and started to collapse: the final collapse will happen in $\sim 3 \ 10^9$ h$^{-1}$ yrs.

    -- We compare our mass estimates on various scales with other results in the literature, finding a general agreement.

    -- We find an indication that the value of the bias between clusters and galaxies in the Shapley Concentration is higher than that reported in literature, confirming the impression that this supercluster is very rich in clusters.

    -- Finally from the comparison with some theoretical scenarios, we find that the Shapley Concentration is consistent with the predictions of the models with more power on large scale (such as Open and $\Lambda$ CDM), while it is inconsistent with the standard CDM normalized to the cluster abundance.

    PAPERS

    Bardelli S., Zucca E., Zamorani G., Moscardini L., Scaramella R., 2000 `` A study of the core of the Shapley Concentration:IV Distribution of intercluster galaxies '' MNRAS 312 540

    Bi-dimensional distribution of galaxies from the COSMOS catalogue in the central part of the Shapley Concentration. Not the two clusters complexes (dominated by the A3558 and A3528 clusters).