Cosmology and cluster halo scaling relations

We explore the effects of dark matter and dark energy on the dynamical scaling properties of galaxy clusters. We investigate the cluster Faber-Jackson (FJ), Kormendy and Fundamental Plane (FP) relations between the mass, radius and velocity dispersion of cluster-sized haloes in cosmological N-body simulations. The simulations span a wide range of cosmological parameters, representing open, flat and closed Universes.

Independently of the cosmology, we find that the simulated clusters are close to a perfect virial state and do indeed define an FP. The fitted parameters of the FJ, Kormendy and FP relationships do not show any significant dependence on (m) and/or (Lambda). One outstanding effect is the influence of (m) on the thickness of the FP.

Following the time evolution of our models, we find slight changes of FJ and Kormendy parameters in high-(m) universe, along with a slight decrease of FP fitting parameters. We also see an initial increase of the FP thickness followed by a convergence to a nearly constant value. The epoch of convergence is later for higher values of (m), while the thickness remains constant in the low-(m) Lambda models. We also find a continuous increase of the FP thickness in the standard cold dark matter cosmology. There is no evidence that these differences are due to the different power spectrum slopes at cluster scales.

From the point of view of the FP, there is little difference between clusters that quietly accreted their mass and those that underwent massive mergers. The principal effect of strong mergers is to significantly change the ratio of the half-mass radius r(half) to the harmonic mean radius r(h).