Statistical Properties of Supercluster-Like Filaments from Cosmological Simulations

Abstract

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, the foam- like cosmic web is subsequently broken into individual supercluster-like groups and further halos which are in accordance to groups with the linking density threshold {\rho}/{\rho}= 1 + {\delta} = 80. By analyzing sets of cosmological simulations with varying cosmological parameters, we find that an universal mass function exists not only for halos but also for low-density supercluster-like groups until the linking density threshold decreases to a density 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 + {\delta} = 16 is in good agreements 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 we define groups identified with 1 + {\delta} = 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.