The origin of 'Great Walls'

TL;DR

This paper introduces a novel semi-analytical model based on the Zel'dovich approximation to explain the formation and large sizes of cosmic 'great walls', emphasizing the role of non-Gaussian and anisotropic fields in their development.

Contribution

It presents a new approach using the Zel'dovich approximation to identify progenitors of large-scale structures, predicting walls exceeding 500 Mpc in size in the universe.

Findings

Model predicts existence of walls larger than 500 Mpc.

Progenitors depend on non-Gaussian and anisotropic fields.

Structures are influenced by linear potential smoothed at current nonlinearity scale.

Abstract

A new semianalytical model that explains the formation and sizes of the 'great walls' - the largest structures observed in the universe is suggested. Although the basis of the model is the Zel'dovich approximation it has been used in a new way very different from the previous studies. Instead of traditional approach that evaluates the nonlinear density field it has been utilized for identification of the regions in Lagrangian space that after the mapping to real or redshift space (depending on the kind of structure is studied) end up in the regions where shell-crossing occurs. The set of these regions in Lagrangian space form the progenitor of the structure and after the mapping it determines the pattern of the structure in real or redshift space. The particle trajectories have crossed in such regions and the mapping is no longer unique there. The progenitor after mapping makes only one stream in the multi-stream flow regions therefore it does not comprise all the mass. Nevertheless, it approximately retains the shape of the structure. The progenitor of the structure in redshift space depends on a few non-Gaussian fields and also it is strongly affected by two anisotropic fields that determine the pattern of great walls as well as their huge sizes. All the fields used in the mappings are derived from the linear potential smoothed at the current scale of nonlinearity which is $R_{nl} = 2.7$ {\hmpc} for the adopted parameters of the \lcdm universe normalized to $\sigma_8 = 0.8$. The model predicts the existence of walls with sizes significantly greater than 500 {\hmpc} that may be found in sufficiently large redshift surveys.