Smooth halos in the cosmic web

TL;DR

This paper introduces entropic measures to quantify the smoothness of dark matter halos within the cosmic web, enabling a clearer transition characterization from halos to the larger web structure.

Contribution

It proposes a novel application of entropic measures linked to multifractal analysis to define and quantify halo smoothness and transition scales.

Findings

Entropic measures effectively characterize the smoothness transition.

Smoothness sizes are distinct from virial radii.

Discreteness parameters influence smoothness measurements.

Abstract

Dark matter halos can be defined as smooth distributions of dark matter placed in a non-smooth cosmic web structure. This definition of halos demands a precise definition of smoothness and a characterization of the manner in which the transition from smooth halos to the cosmic web takes place. We introduce entropic measures of smoothness, related to measures of inequality previously used in economy and with the advantage of being connected with standard methods of multifractal analysis already used for characterizing the cosmic web structure in cold dark matter N-body simulations. These entropic measures provide us with a quantitative description of the transition from the small scales portrayed as a distribution of halos to the larger scales portrayed as a cosmic web and, therefore, allow us to assign definite sizes to halos. However, these "smoothness sizes" have no direct relation to the virial radii. Finally, we discuss the influence of N-body discreteness parameters on smoothness.