# Voids and Superstructures: correlations and induced large-scale velocity flows

## TL;DR

This study investigates the large-scale dynamics of cosmic voids and galaxies relative to superstructures, revealing infall patterns and velocity flows that are consistent between simulations and observational data.

## Contribution

It introduces a correlation measure to analyze void-superstructure relationships and demonstrates the consistency of these dynamical behaviors in both simulations and SDSS data.

## Key findings

- Void-in-clouds are closer to superstructures than void-in-voids.
- Galaxies in void shells infall towards superstructures, with velocities depending on their position.
- Simulation results are confirmed by SDSS observational data.

## Abstract

The expanding complex pattern of filaments, walls and voids build the evolving cosmic web with material flowing from underdense onto high density regions. 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 voids-in-clouds (S-types) preferentially located closer to superstructures than voids-in-voids (R-types) although we obtain that voids within $\sim40~\mathrm{Mpc}\,\mathrm{h}^{-1}$ of superstructures are infalling in a similar fashion 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.