Structure of superclusters and supercluster formation - III. Quantitative study of the Local Supercluster

We have studied the structure of the Local Supercluster using data on the three-dimensional distribution of galaxies, based on the redshift compilations by H. Rood and J. Huchra. Several quantitative methods have been used – correlation and multiplicity analyses, clustering and percolation methods. The observed distributions have been compared with model distributions, obtained from simulated Poisson, adiabatic and simple hierarchical samples. We have found that galaxy systems of different size and density contrast can be separated in the Local Supercluster by cluster analysis. The supercluster can be divided into clusters and strings of galaxies. Clusters are density enhancements in strings, and strings are constituent parts of superclusters. Galaxy strings form bridges between superclusters and join all superclusters to a single infinite network. Thus systems of galaxies are not isolated objects. Simple hierarchical models as well as the Poisson model have properties completely different from the observed distribution, whereas adiabatic models fit the observations much better. However, the adiabatic model has too few systems of intermediate richness. On the other hand, our simple hierarchical model does not include dynamical evolution. Thus it is premature to draw final conclusions concerning the formation of superclusters. The observed distribution has a characteristic scale-length, corresponding to the transition from the central cluster to strings of galaxies; in the correlation function there is a pronounced bump at this scale.