Getting the tiger by the tail: Probing the turnaround radius of structures with outer halo density profiles

TL;DR

This paper introduces a semi-analytical model to characterize the outer density profiles of dark matter halos, emphasizing the significance of the turnaround radius as a key transition scale, and proposes a universal measurement method.

Contribution

The authors develop a robust spherical collapse model that links the turnaround radius to the outer halo density profile, offering a new universal test for structure analysis.

Findings

Model remains stable under parameter variations

Turnaround radius effectively marks the transition in density profiles

Proposed geometrical test for measuring the turnaround radius

Abstract

In this paper we develop a new semianalytical approach to quantifying the density profile of outer dark matter halos, motivated by the remarkable universality those profiles, for a wide range of dynamical parameters of the inner halos. We show that our minimalist spherical collapse based model is robust under significant variations of its input parameters around the currently known values and we identify the turnaround radius as the most important scale of the problem. Based on that observation, we argue that the turnaround radius accurately represents the transition to the external density profile, and we provide a universal test based on geometrical characteristics of the outer profile as a proposal for measuring the turnaround radius of structures.