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Register a new userA study of the core of the Shapley Concentration: IV. Distribution of intercluster galaxies and supercluster properties
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(abridged) We present the results of a redshift survey of intercluster galaxies in the central region of the Shapley Concentration supercluster, aimed at determining the distribution of galaxies in between obvious overdensities. Our sample is formed by 442 new redshifts, mainly in the b_J magnitude range 17-18.8. Adding the data from our redshift surveys on the A3558 and A3528 complexes, which are close to the geometrical centre of this supercluster, we obtain a total sample of ~2000 radial velocities. Using the 1440 galaxies of our total sample in the magnitude range 17 - 18.8, we reconstructed the density profile in the central part of the Shapley Concentration; moreover we detected another significant overdensity at ~30000 km/s (dubbed S300). We estimate the total overdensity in galaxies, the mass and the dynamical state of these structures, and discuss the effect of considering a bias between the galaxy distribution and the underlying matter. We find an indication that the value of the bias between clusters and galaxies in the Shapley Concentration is higher that 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 existence of the Shapley Concentration is more consistent with the predictions of the models with a matter density parameter <1, such as open CDM and Lambda CDM.
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We present the results of a study of the spectral properties of galaxies in the central part of the Shapley Concentration, covering an extremely wide range of densities, from the rich cluster cores to the underlying supercluster environment. Our sample is homogeneous, in a well defined magnitude range (17=<b_J=<18.8) and contains ~1300 spectra of galaxies at the same distance, covering an area of ~26 sq.deg. These characteristics allowed an accurate spectral classification, that we performed using a Principal Components Analysis technique. This spectral classification, together with the [OII] equivalent widths and the star formation rates, has been used to study the properties of galaxies at different densities: cluster, intercluster (i.e. galaxies in the supercluster but outside clusters) and field environment. No significant differences are present between samples at low density regimes (i.e. intercluster and field galaxies). Cluster galaxies, instead, not only have values significantly different from the field ones, but also show a dependence on the local density. Moreover, a well defined morphology-density relation is present in the cluster complexes, although these structures are known to be involved in major merging events. Also the mean equivalent width of [OII] shows a trend with the local environment, decreasing at increasing densities, even if it is probably induced by the morphology-density relation. Finally we analyzed the mean star formation rate as a function of the density, finding again a decreasing trend (at ~ 3sigma significance level). Our analysis is consistent with the claim of Balogh et al. (1998) that the star formation in clusters is depressed.
We present the results of a redshift survey of both cluster and intercluster galaxies in the central part of the Shapley Concentration, the richest supercluster of clusters in the nearby Universe, consisting of ~2000 radial velocities. We estimate the total overdensity in galaxies of the supercluster and its mass and we discuss the cosmological implications of these results. Moreover, using a Principal Components Analysis technique, we study the influence of the cluster and supercluster dynamics on the galaxy spectral morphology.
We present new results of our wide-field redshift survey of galaxies in a 182 square degree region of the Shapley Supercluster (SSC) based on observations with the FLAIR-II spectrograph on the UK Schmidt Telescope. We present new measurements to give a total sample of redshifts for 710 bright (R<16.6) galaxies, of which 464 are members of the SSC (8000<v<18000 kms). Our data reveal that the main plane of the SSC extends further than previously realised, filling the whole extent of our survey region of 10 degrees by 20 degrees on the sky (35 Mpc by 70 Mpc). There is also a significant structure associated with the slightly nearer Abell 3571 cluster complex with a caustic structure evident out to a radius of 6 Mpc. These galaxies seem to link two previously identified sheets of galaxies and establish a connection with a third one at v=15000 kms. They also tend to fill the gap of galaxies between the foreground Hydra-Centaurus region and the more distant SSC. We calculate galaxy overdensities of 5.0+/-0.1 over the 182 square degree region surveyed and 3.3+/-0.1 in a 159 square degree region excluding rich clusters.
The Shapley Concentration is the richest supercluster of clusters in the nearby universe and its core is a remarkable complex formed by the ACO clusters A3558, A3562 and A3556, and by the two minor groups SC 1327-312 and SC 1329-314. This structure has been studied in various wavelength bands, revealing that it is probably dynamically very active. In this paper we present 174 new galaxy redshifts in this cluster complex, which are added to the sample of 540 already existing velocities. The large number of redshifts permits a more accurate and robust analysis of the dynamical parameters of the clusters. In particular, we discuss the complex velocity distribution of A3558, the bimodal distribution of A3556 and SC 1329-313, and calculate the mean velocity and velocity dispersion of A3562. Moreover, for the three ACO clusters we derive the luminosity functions adopting a new fitting technique, which takes into account the galaxy density profiles.
We present the results of a galaxy redshift survey in the central region of the Shapley Concentration. Our total sample contains ~2000 radial velocities of galaxies both in the clusters and in the intercluster field. We reconstruct the density profile of this supercluster, calculate its overdensity and total mass. Moreover we detect a massive structure behind the Shapley Concentration, at ~30000 km/s.
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