Nature and distribution of dark matter: 2 binaries, groups and clusters

The mass-radius relationship for aggregates of galaxies, viz. binaries, small groups and clusters is studied. The data are subjected to a simple best-fit analysis similar to the one carried out earlier for individual field galaxies. The analysis shows that: (i) The data on binary galaxies are consistent with the assumption that binaries are just two galaxies, each with an individual isothermal (M ∞ R) dark matter halo, moving under the mutual gravitational attraction. (ii) The data on the groups of galaxies are too scattered to obey a single power-law relation of the form M=kRsup(n) with any degree of reliability. (iii) The data on groups and clusters fit better with a law of the form M=AR3+BR. This form suggests the existence of two components in dark matter-one which is clustered around the galaxies (M ∞ R) and another which is distributed smoothly (M ∞ R3). The smooth distributions becomes significant only at scales >= 1 Mpc and hence does not affect binaries significantly. The theoretical implications of this analysis are briefly discussed. (author). 20 refs., 3 figs