Assembly History and Internal Structure of Cluster Cold Dark Matter Haloes

TL;DR

This study uses simulations to analyze the growth and internal structure of galaxy cluster dark matter haloes, revealing their inside-out growth, active evolution, and less stable density profiles compared to galactic haloes.

Contribution

It provides new insights into the assembly history and internal dynamics of cluster haloes, highlighting differences from galactic haloes and their implications.

Findings

Cluster haloes grow inside-out, with major mergers shaping the core.

Most mass in the inner region is accreted after redshift 3.

Density profiles of cluster haloes are less stable over time.

Abstract

We use the Phoenix simulations to study the mass assembly history and internal structures of cluster dark matter haloes ($M_{200} \gtrsim 5\times 10^{14} h^{-1}{\rm M}_\odot$). We confirm that cluster haloes grow inside-out, similar to galactic haloes. Major merger events dominate the growth of the internal region and minor mergers/diffuse accretion shape the outskirts. However, compared to galactic haloes, cluster haloes tend to have a younger and more actively evolving inner region. On average, the majority of mass (> 80%) in the inner region ($R< 0.1 r_{200}$) of Phoenix haloes is accreted after $z = 3$, while for galactic haloes, most mass in the central region has already been accreted before $z=6$. The density profiles of cluster haloes are less stable than those of galactic haloes over different radii. The enclosed mass within $50$ or $150$ kpc of all Phoenix haloes evolves substantially in the past ${\sim} 7$ Gyr, while galactic haloes remained stable during the same period. We suggest that the relatively younger and more active state explains the various observations of cluster haloes, especially in central regions.