Cinthia Ragone-Figueroa, Manolis Plionis
Monthly Notices of the Royal Astronomical Society, Volume 377, Issue 4, June 2007, Pages 1785–1794
Publication year: 2007

Summary 

We use group-sized haloes, with masses in the range 1013 < M < 2 × 1014h−1 M, identified with a ‘friends of friends’ (FOF) algorithm in a concordance Λ cold dark matter (ΛCDM) GADGET2 (dark matter only) simulation to investigate the dependence of halo properties on the environment at z= 0. The study is carried out using samples of haloes at different distances from their nearest massive cluster halo, considered as such if its mass is larger than the upper limit of the above halo mass range (i.e. M≥ 2 × 1014h−1 M). We find that the fraction of haloes with substructure typically increases in high-density regions. The halo mean axial ratio 〈c/a〉 also increases in overdense regions, a fact which is true for the whole range of halo mass studied. This can be explained as a reflection of an earlier halo formation time in high-density regions, which gives haloes more time to evolve and become more spherical. Moreover, this interpretation is supported by the fact that, at a given halo–cluster distance, haloes with substructure are more elongated than their equal mass counterparts with no substructure, reflecting that the virialization (and thus sphericalization) process is interrupted by merger events. The velocity dispersion of low-mass haloes with strong substructure shows a significant increase near massive clusters with respect to equal mass haloes with low levels of substructure or with haloes found in low-density environments. The alignment signal between the shape and the velocity ellipsoid principal axes decreases going from lower to higher density regions, while such an alignment is stronger for haloes without substructure. We also find, in agreement with other studies, a tendency of halo major axes to be aligned and of minor axes to lie roughly perpendicular with the orientation of the filament within which the halo is embedded, an effect which is stronger in the proximity of the massive clusters.