The evolution of dark matter halo properties in clusters, filaments, sheets and voids

Abstract

We use a series of high-resolution N-body simulations of the concordance cosmology to investigate the redshift evolution since z = 1 of the properties and alignment with the large-scale structure (LSS) of haloes in clusters, filaments, sheets and voids. We find that (i) once a rescaling of the halo mass with M*(z), the typical mass scale collapsing at redshift z, is performed, there is no further significant redshift dependence in the halo properties; (ii) the environment influences the halo shape and formation time at all investigated redshifts for haloes with masses M ≲ M* and (iii) there is a significant alignment of both spin and shape of haloes with filaments and sheets. In detail, at all redshifts up to z = 1: (a) haloes with masses below ∼ M* tend to be more oblate when located in clusters than in the other environments; this trend is reversed at higher masses: above about M*, haloes in clusters are typically more prolate than similar massive haloes in sheets, filaments and voids. (b) The haloes with M ≳ M* in filaments spin more rapidly than similar mass haloes in clusters; haloes in voids have the lowest median spin parameters. (c) Haloes with M ≲ M* tend to be younger in voids and older in clusters. (d) In sheets, halo spin vectors tend to lie preferentially within the sheet plane independent of halo mass; in filaments, instead, haloes with M ≲ M* tend to spin parallel to the filament and higher mass haloes perpendicular to it. For halo masses M ≳ M*, the major axis of haloes in filaments and sheets is strongly aligned with the host filament or the sheet plane, respectively. Such halo-LSS alignments may be of importance in weak lensing analyses of cosmic shear. A question that is opened by our study is why, in the 0 < z < 1 redshift regime that we have investigated, the mass scale for gravitational collapse, M*, sets roughly the threshold below which the LSS environment either begins to affect, or reverses, fundamental properties of dark matter haloes. © 2007 RAS.