Voids and Superstructures: correlations and induced large–scale velocity flows

The cosmic web is an expanding complex pattern of filaments, walls and voids, where matter flows from underdense regions towards the high density peaks. Recently, we showed that voids have non negligible global motions, consistent with these large–scale flows. Here we explore the dynamical behaviour of voids and galaxies in void shells relative to neighboring overdense superstructures, using the Millenium Simulation and the main galaxy catalogue in Sloan Digital Sky Survey data. We define a correlation measure to estimate the tendency of voids to be located at a given distance from a superstructure. We find that voids–in–clouds (S–types) are preferentially located closer to superstructures than voids–in–voids (R–types), as expected, but allowing a better understanding of void evolution according to their surroundings. Following this approach, we also find that voids within ∼ 40Mpc/h of a superstructure are infalling, independently of void type. Galaxies residing in void shells show infall towards the closest superstructure, along with the void global motion, with a differential velocity component depending on their relative position in the shell with respect to the direction to the superstructure. This effect is produced by void expansion and therefore is stronger for R–types. We also find that galaxies in void shells facing the superstrucure flow towards the overdensities faster than galaxies elsewere at the same relative distance to the superstructure. The results obtained for the simulation are also reproduced for the SDSS data with a linearized velocity field implementation.