Void Scaling and Void Profiles in CDM Models

Received ABSTRACT An analysis of voids using cosmological N-body simulations of cold dark matter (CDM) models is presented. It employs a robust statistics of voids, that was recently applied to discriminate between data from the Las Campanas Redshift Survey (LCRS) and different cosmological models. Here we extend the analysis to 3D and show that typical void sizes D in the simulated galaxy samples obey a linear scaling relation with the mean galaxy separation λ: D = D 0 + ν × λ. It has the same slope ν as in 2D, but with lower absolute void sizes. The scaling relation is able to discriminate between different cosmologies. For the best standard ΛCDM model, the slope of the scaling relation for voids in the dark matter halos is too steep as compared to the LCRS, with too small void sizes for well sampled data sets. By considering a range of CDM simulations we further investigate the scaling relation for voids within the distribution of dark matter halos and other properties of underdense regions. The scaling relation of voids for dark matter halos with increasing mass thresholds is even steeper than that for samples of galaxy-mass halos where we sparse sample the data. This shows the stronger clustering of more massive halos. Further, we find a correlation of the void size to its central and environmental average density. We study the evolution of the void size distribution of dark matter halos at redshifts up to z = 3 measuring the sizes in comoving coordinates. While there is little sign of an evolution in samples of small DM halos with v circ ≈ 90 km/s, voids in halos with circular velocity over v circ = 200 km/s are larger at redshift z = 3 due to the smaller halo number density. The flow of dark matter from the underdense to overdense regions in an early established network of large scale structure is also imprinted in the evolution of the density profiles with a relative density decrease in void centers by ∆(ρ/ ¯ ρ) ≃ 0.18 per redshift unit between z = 3 and z = 0. Key words: cosmology: dark matter – galaxies: formation – large scale structure of the universe.