Cosmological alignment of clusters of galaxies with their surroundings - a problem for cold dark matter?

The shapes and orientations of rich clusters of galaxies formed in various cosmogonic scenarios are studied by means of high-resolution N-body simulations and compared with observations. The ellipticities of the main bodies of the simulated clusters are found to be fairly independent of the initial conditions and therefore cannot provide a very sensitive test for cosmology. On the other hand, the orientations of clusters with respect to the galaxy distribution on larger scales are found to provide a very useful test. A pronounced tendency for alignment is found in the pancake scenario, on scales up to at least 10/h Mpc, and presumably further. Weaker, although still significant, alignments are also seen in the n = -2 hierarchical case and the hybrid scenario, while no detectable alignments are found for either the n = 0 or n = -1 hierarchical scenarios, which approximates cold dark matter on cluster scales. 55 references