Abstract
In this paper, we study large-scale structures from numerical simulations, paying particular attention to supercluster-like structures. A grid-density-contour-based algorithm is adopted to locate connected groups. With the increase of the linking density threshold from the cosmic average density, the foam-like cosmic web is subsequently broken into individual supercluster-like groups and further halos. To be in accordance with normal friends-of-friends halos with the linking length of 0.2 in units of the average separation of particles, halos in this paper are defined as groups with the linking density threshold ρ/\bar{ρ}=1+δ =80, where ρ is the grid density, and \bar{\rho } is the average mass density of the universe. Groups with lower linking densities are then generally referred to as supercluster-like groups. By analyzing sets of cosmological simulations with varying cosmological parameters, we find that a universal mass function exists not only for halos but also for low-density supercluster-like groups until the linking density threshold decreases to 1 + δ ~ 8 where the global percolation of large-scale structures occurs. We further show that the mass functions of different groups can be well described by the Jenkins form with the parameters being dependent on the linking density threshold. On the other hand, these low-density supercluster-like groups cannot be directly associated with the predictions from the excursion set theory with effective barriers obtained from dynamical collapse models, and the peak-exclusion effect must be taken into account. Including such an effect, the mass function of groups with the linking density threshold 1 + δ = 16 is in good agreement with that from the excursion set theory with a nearly flat effective barrier. A simplified analysis of the ellipsoidal collapse model indicates that the barrier for collapses along two axes to form filaments is approximately flat in scales. Thus, in our analyses, we define groups identified with 1 + δ = 16 as filaments. We then further study the halo-filament conditional mass function and the filament-halo conditional mass function and compare them with the predictions from the two-barrier excursion set theory. The shape statistics for filaments are also presented.
Author
Yan, Heling; Fan, Zuhui
Journal
Astrophysical Journal
Paper Publication Date
March 2011
Paper Type
Astrostatistics