Coming of Age in the Dark Sector: How Dark Matter Haloes grow their Gravitational Potential Wells

TL;DR

This paper investigates how dark matter haloes grow their mass and gravitational potential wells, revealing that potential well growth precedes mass assembly and proposing a universal model for their growth histories.

Contribution

It introduces a new universal model for halo mass accretion and potential well growth histories applicable across different masses and cosmologies.

Findings

Potential well growth precedes mass assembly.

Maximum circular velocity reaches half its current value after only 2% mass accretion.

Universal form of mass accretion histories enables model predictions without simulations.

Abstract

We present a detailed study of how dark matter haloes assemble their mass and grow their (central) potential well. We characterize these via their mass accretion histories (MAHs) and potential well growth histories (PWGHs), which we extract from the Bolshoi simulation and from semi-analytical merger trees supplemented with a method to compute the maximum circular velocity, Vmax, of progenitor haloes. The results of both methods are in excellent agreement, both in terms of the average and the scatter. We show that the MAH and PWGH are tightly correlated, and that growth of the central potential precedes the assembly of mass; the maximum circular velocity is already half the present day value by the time the halo has accreted only 2 percent of its final mass. Finally, we demonstrate that MAHs have a universal form, which we use to develop a new and improved universal model that can be used to compute the average or median MAH and PWGH for a halo of any mass in any LCDM cosmology, without having to run a numerical simulation or a set of halo merger trees.