Imprints of mass accretion on properties of galaxy clusters

A large-scale smoothed particle hydrodynamics (SPH) plus N-body simulation (GADGET) of the concordance cold dark matter (CDM) universe is used to investigate orientation and angular momentum of galaxy clusters at z = 0 in connection with their recent accretion histories. The basic cluster sample comprises the 3000 most massive friends-of-friends (FoF) haloes found in the 500 h -1 Mpc simulation box. Two disjoint subsamples are constructed, using the mass ratio of the two most massive progenitors at z = 0.5 m 2 /m 1 (m 1 m 2 ), namely a recent major merger sample and a steady accretion mode sample. The mass of clusters in the merger sample is on average 43 per cent larger than the mass of the two progenitors (m 1 + m 2 ), whereas in the steady accretion mode sample a smaller increase of 25 per cent is found. The separation vector connecting the two most massive progenitor haloes at z = 0.5 is strongly correlated with the orientation of the cluster at z = 0. The angular momentum of the clusters in the recent major merger sample tends to be parallel to orbital angular momentum of the two progenitors, whereas the angular momentum of the steady accretion mode sample is mainly determined by the angular momentum of the most massive progenitor. The long-range correlations for the major and the minor principal axes of cluster pairs extend to distances of 100 h -1 Mpc. Weak angular momentum correlations are found for distances 20 h -1 Mpc. Within these ranges, the major axes tend to be aligned with the connecting line of the cluster pairs, whereas minor axes and angular momenta tend to be perpendicular to this line. A separate analysis of the two subsamples reveals that the long-range correlations are independent of the mass accretion mode. Thus, orientation and angular momentum of galaxy clusters is mainly determined by the accretion along the filaments independently of the particular accretion mode.