The alignment of clusters using large-scale simulations

The alignment of clusters of galaxies with their nearest neighbours and between clusters within a supercluster is investigated using simulations of 512(3) dark matter particles for Lambda CDM and tau CDM cosmological models. Strongly significant alignments are found for separations of up to 15 h(-1) Mpc in both cosmologies, but for the Lambda CDM model the alignments extend up to separations of 30 h(-1) Mpc. The effect is strongest for nearest neighbours, but is not significant enough to be useful as an observational discriminant between cosmologies. As a check of whether this difference in alignments is present in other cosmologies, smaller simulations with 256(3) particles are investigated for four different cosmological models. Because of poor number statistics, only the standard CDM model shows indications of having different alignments from the other models.