A new catalogue of multiple galaxies in the Local Supercluster

A new approach is suggested which makes use of the individual properties of galaxies, for the identification of small galaxy groups in the Local Supercluster. The criterion is based on the assumption of closed orbits of the companions around the dominating group member within a zero velocity sphere.The criterion is applied to a sample of 6321 nearby galaxies with radial velocities V0 ≤ 3000 km s−1. These 3472 galaxies have been assigned to 839 groups that include 55% of the sample considered. For the groups identified by the new algorithm (with k ≥ 5 members) the median velocity dispersion is 86 km s−1, the median harmonic radius is 247 kpc, the median crossing time is 0.08(1/H), and the median virial-mass-to-light ratio is 56 M⊙/L⊙.

Dark Matter in Groups and Clusters of Galaxies

Samples of groups, clusters and superclusters of galaxies have been collected from existing catalogs. The group sample consisted of 70 systems, the list of clusters contains 50 systems, and there are five superclusters. Kinematical and dynamical characteristics are obtained — elongation (along the line of sight, RA and Dec), velocity statistics, total luminosity, harmonic radius, mean pair separation, crossing time, virial mass … We have compared some of the observational features with dynamical models of groups, clusters and superclusters. Aarseth's (1985) code is used.

Triple Galaxies and a Hidden Mass Problem

We consider a homogeneous sample of 84 triple systems of galaxies with components brighter than m = 15.7, located in the northern sky and satisfying an isolation criterion with respect to neighboring galaxies in projection. The distributions of basic dynamical parameters for triplets have median values as follows: radial velocity dispersion 133 km/s, mean harmonic radius 63 kpc, absolute magnitude of galaxies MB = —20.38, crossing time τ = 0.04 H−1. For different ways of estimation the median mass-to-luminosity ratio is (20 – 30)f⊙.A comparison of the last value with the ones for single and binary galaxies shows the presence of a virial mass excess for triplets by a factor 4. The mass-to-luminosity ratio is practically uncorrelated with linear size of triplets or with morphological types of their components.We note that a significant part of the virial excess may be explained by the presence of nonisolated triple configurations in the sample, which are produced by debris of more populous groups of galaxies.