Galaxy groups a intermediate redshifts

The mean number density of galaxies around group centers falls nearly as a power law with r^-2.5^ and has no well-defined core. The projected velocity dispersion of galaxies around group centers is either flat or slowly rising outward. The combination of a steeper than isothermal density profile and the outward rising velocity dispersion implies that the mass-to-light ratio of groups rises with radius if the velocity ellipsoid is isotropic but could be nearly constant if the galaxy orbits are nearly circular.

Such strong tangential anisotropy is not supported by other evidence. Although the implication of a rising M/L must be viewed with caution, it could naturally arise through dynamical friction acting on the galaxies in a background of "classical" collisionless dark matter.