The connection between dark matter, internal motions and configurational properties of triple galaxies

Abstract

Abstract. Numerical simulations of the dynamics of triplets of galaxies show that virial estimations of the individual masses of triplets are unreliable because of strong nonsteadiness of these groups and projection effects. However, the mass of a typical small galaxy group can be estimated statistically, from data on a whole homogeneous ensemble of groups such as, for example, Karachentsev's Catalogue of compact galaxy triplets. The characteristic total mass of a triplet from this catalogue is 4 -7 times greater than the visible mass when the standard mass-to-light ratio is assumed. This suggests the presence of some considerable amount of dark matter even in these compact triplets. In wide triplets of galaxies the amount of dark matter may be significantly larger. The presence of distributed dark matter makes motions of galaxies in triplets more stochastic. In this case the existence of long-lived hierarchical configurations (temporary binaries) in triple systems becomes much less probable than without dark matter. The analysis of internal motions of galaxies in triplets and their configurations may be interpreted as additional non-dynamical evidence of the presence of dark matter in galaxy triplets.