Imprints of Dark Energy on Cosmic Structure Formation: III. Sparsity of Dark Matter Halo Profiles

TL;DR

This paper investigates how Dark Energy influences the structure of Dark Matter halos, introducing a new observable called halo sparsity that varies with Dark Energy models and can serve as a cosmological probe.

Contribution

It introduces the halo sparsity as a new non-parametric measure of halo profiles and demonstrates its sensitivity to Dark Energy, offering a novel way to test cosmological models.

Findings

Halo sparsity is nearly independent of halo mass.

Sparsity can be inferred with high precision from halo mass functions.

Sparsity varies significantly with different Dark Energy models.

Abstract

We study the imprint of Dark Energy on the density profile of Dark Matter halos using a set of high-resolution large volume cosmological N-body simulations from the Dark Energy Universe Simulation Series (DEUSS). We first focus on the analysis of the goodness-of-fit of the Navarro-Frenk-White (NFW) profile which we find to vary with halo mass and redshift. We also find that the fraction of halos ill-fitted by NFW varies with cosmology, thus indicating that the mass assembly of halos with perturbed density profiles carries a characteristic signature of Dark Energy. To access this information independently of any parametric profile, we introduce a new observable quantity: the halo sparsity $s_\Delta$. This is defined as the mass ratio $M_{200}/M_\Delta$, i.e. the ratio of mass inside a sphere of radius $r_{200}$ to that contained within a radius $r_\Delta$, enclosing 200 and $\Delta$ times the mean matter density respectively. We find the average sparsity to be nearly independent of the total halo mass, while its value can be inferred to better than a few percent from the ratio of the integrated halo mass functions at overdensities $\Delta$ and 200 respectively. This provides a consistency relation that can validate observational measurements of the halo sparsity. Most importantly, the sparsity significantly varies with the underlying Dark Energy model, thus providing an alternative cosmological probe.