Cosmological shock waves: clues to the formation history of haloes

TL;DR

This paper analyzes cosmological shock waves in simulations to understand their role in the formation and evolution of cosmic haloes, revealing distinct shock classes and a new scaling relation linked to halo history.

Contribution

It introduces a novel analysis of shock wave morphology and properties in cosmological simulations, including a new scaling relation between Mach number and halo mass.

Findings

Shocks are classified into internal weak and external strong types.

The shock distribution follows a double power law with a Mach number break at 20.

A new scaling relation links halo Mach numbers with their virial masses.

Abstract

Shock waves developed during the formation and evolution of cosmic structures encode crucial information on the hierarchical formation of the Universe. We analyze an Eulerian AMR hydro + N-body simulation in a $\Lambda$CDM cosmology focused on the study of cosmological shock waves. The combination of a shock-capturing algorithm together with the use of a halo finder allows us to study the morphological structures of the shock patterns, the statistical properties of shocked cells, and the correlations between the cosmological shock waves appearing at different scales and the properties of the haloes harbouring them. The shocks in the simulation can be split into two broad classes: internal weak shocks related with evolutionary events within haloes, and external strong shocks associated with large-scale events. The shock distribution function contains information on the abundances and strength of the different shocks, and it can be fitted by a double power law with a break in the slope around a Mach number of 20. We introduce a generalised scaling relation that correlates the average Mach numbers within the virial radius of haloes and their virial masses. In this plane, haloes occupy different areas according to their early evolutionary histories: those with a quiet evolution have an almost constant Mach number independently of their masses, whereas haloes undergoing significant merger events very early in their evolution show a linear dependence with their masses. At high redshift, the halo distribution in this scaling relation forms a L-like pattern that changes due to the evolution of the haloes. The analysis of the propagation speed and size of the shock waves around haloes could give some hints on the formation time and main features of the haloes. (Abridged)