Cluster infall in the concordance ΛCDM model

We perform statistical analyses of the infall of dark matter on to clusters in numerical simulations within the concordance ACDM (cold dark matter) model. By studying the infall profile around clusters of different mass, we find a linear relation between the mass and maximum infall velocities which reach similar to 900 km s(-1) for the most massive groups. The maximum infall velocity and the group mass follow a suitable power-law fit of the form V-inf(max) = (M/m(0))(y). By comparing the measured infall velocity to the linear infall model with an exponential cut-off introduced by Croft et al., we find that the best agreement is obtained for a critical overdensity delta(c) = 45. We study the dependence of the direction of infall with respect to the cluster centres, and find that in the case of massive groups, the maximum alignment occurs at scales r similar to 6 h(-1) Mpc. We obtain a logarithmic power-law relation between the average infall angle and the group mass. We also study the dependence of the results on the local dark matter density, finding a remarkable difference in the dynamical behaviour of low- and high-density particles.