The Galaxy Group/cosmology Connections

Groups of galaxies are highly linked to cosmology: 1) groups are tidally destroyed by the tidal eld of the cluster they fall into; 2) spherical infall leads to the young cosmo-dynamical state of loose groups, a fundamental surface for groups, 0 ' 0:3, and the mixed nature of compact groups (virialized groups, groups at full collapse, and chance alignments within collapsing loose groups, for decreasing compact group velocity dispersion) ; 3) X-ray analyses lead to 0 < 0:5.