Dark matter content in pairs and triplets

For the samples of galaxy pairs and triplets which were defined by geometric method based on the high-order 3D Voronoi tessellation, in our papers Elyiv et al. (2009) and Melnyk et al. (2009) we found the dependence of isolation parameters (p and t) of galaxy system on the value of virial mass-to-luminosity ratio (Mvir/L), fig. 3. Figs. 4 and 5 present the examples of pairs and triplets within different environments (i.e. the values of isolation papameters) in depence on the value of Mvir/L, marked in fig. 3a and 3b by numbers 1, 2 and 3. The median values of mass-to-luminosity ratio are 12 M⊙/L⊙  for the isolated pairs and 44 M⊙/L⊙  for the isolated triplets; 7 (8) M⊙/L⊙  for the most compact pairs (triplets). Fig. 6 presents the dependence of M/L on luminosity. It can be seen that mass grows faster than luminosity in different scales.

We also conclude that in such small groups as pairs and triplets the segregation by luminosity is clearly observed: galaxies in the isolated pairs and triplets are on average two times more luminous than isolated galaxies.