Void Formation: Does the Void-in-Cloud Process Matter?

Abstract

Abstract We investigate the basic properties of voids from high resolution, cosmological N-body simulations of Λ–dominated cold dark matter (ΛCDM) models, in order to compare with the analytical model of Sheth and van de Weygaert (SvdW) for void statistics. For the subsample of five dark matter simulations in the ΛCDM cosmology with box sizes ranging from 1000h−1Mpc to 8 h−1Mpc, we find that the standard void–in–cloud effect is too simplified to explain several properties of identified small voids in simulations. (i) The number density of voids is found to be larger than the prediction of the analytical model up to 2 orders of magnitude below 1h−1Mpc scales. The Press-Schechter model with the linear critical threshold of void δv = −2.71, or a naive power law, is found to provide an excellent agreement with the void size function, suggesting that the void-in-cloud effect does not suppress as much voids as predicted by the SvdW model. (ii) We then measured the density and velocity profiles of small voids, and find that they are mostly partially collapsing underdensities, instead of being completely crushed in the standard void–in–cloud scenario. (iii) Finally, we measure the void distributions in four different tidal environments, and find that the void–in-void effect alone can explain the correlation between distribution and environments, whereas the void–in–cloud effect is only weakly influencing the abundance of voids, even in filaments and clusters.