Wide triplets of galaxies: collapse on spatial scales of similar to 1 Mpc

We study triple systems of galaxies with mean projected harmonic separation similar or equal to0.6h(-1)Mpc [h = H/(75 km s(-1) Mpc(-1))]. We call the systems 'wide triplets', in contrast to compact triplets with mean projecte d harmonic separation similar or equal to0.04 h(-1) Mpc, studied by Karache ntsev et al. Data are taken for 108 wide triplets from a list compiled by T rofimov & Chernin; at least one-third of them are considered to be probably isolated physical systems. With typical crossing times of about the Hubble rime, the wide triplets seem to be in a state of ongoing collapse. This is confirmed by a set of computer models which simulate well the observationa l characteristics of the ensemble of wide triplets. The simulations also gi ve a statistical estimate of the total mass of a typical wide triplet: it p roves to be similar or equal to 10(13) M-circle dot. This figure indicates that the dark matter mass is 15-30 times the mass of baryonic matter in the systems. The dynamics of wide triplets, as well as their dark matter conte nt, provide new direct cosmological constraints by establishing that hierar chical evolution is occurring on a mass scale of similar to 10(13) M-circle dot and a spatial scale of similar to1 Mpc.