Reconstructing matter profiles of spherically compensated cosmic regions in $\Lambda$CDM cosmology

TL;DR

This paper introduces CoSpheres, a model for cosmic voids and overdensities in $\\Lambda$CDM cosmology, enabling precise profile reconstruction and offering new insights into large-scale cosmic structures and their evolution.

Contribution

It extends the peak model to define and analyze spherically compensated cosmic regions, providing an analytical framework for their profiles and evolution in cosmological simulations.

Findings

High-accuracy profile reconstruction until z=0 in simulations

Analytical solutions for non-linear dynamics around compensation radius

Identification of correlations between local extrema and large-scale environment

Abstract

The absence of a physically motivated model for large scale profiles of cosmic voids limits our ability to extract valuable cosmological information from their study. In this paper, we address this problem by introducing the spherically compensated cosmic regions, named CoSpheres. Such cosmic regions are identified around local extrema in the density field and admit a unique compensation radius $R_1$ where the internal spherical mass is exactly compensated. Their origin is studied by extending the standard peak model and implementing the compensation condition. Since the compensation radius evolves as the Universe itself, $R_1(t)\propto a(t)$, CoSpheres behave as bubble Universes with fixed comoving volume. Using the spherical collapse model, we reconstruct their profiles with a very high accuracy until $z=0$ in N-body simulations. CoSpheres are symmetrically defined and reconstructed for both central maximum (seeding haloes and galaxies) and minimum (identified with cosmic voids). We show that the full non linear dynamics can be solved analytically around this particular compensation radius, providing useful predictions for cosmology. This formalism highlights original correlations between local extremum and their large scale cosmic environment. The statistical properties of these spherically compensated cosmic regions and the possibilities to constrain efficiently both cosmology and gravity will be investigated in companion papers.