Cosmological Shocks in Adaptive Mesh Refinement Simulations and the Acceleration of Cosmic Rays

TL;DR

This study uses adaptive mesh refinement simulations to analyze cosmological shocks, revealing their distribution, evolution, and role in accelerating cosmic rays, with implications for galaxy cluster physics.

Contribution

First application of adaptive mesh refinement to cosmological shock analysis, introducing a new shock-finding algorithm and linking shock properties to cosmic ray acceleration.

Findings

Shock Mach number distribution varies with structure formation stages.

Cosmic ray acceleration is significant in galaxy clusters.

Large simulation volume provides detailed shock statistics.

Abstract

We present new results characterizing cosmological shocks within adaptive mesh refinement N-Body/hydrodynamic simulations that are used to predict non-thermal components of large-scale structure. This represents the first study of shocks using adaptive mesh refinement. We propose a modified algorithm for finding shocks from those used on unigrid simulations that reduces the shock frequency of low Mach number shocks by a factor of ~3. We then apply our new technique to a large, (512 Mpc/h)^3, cosmological volume and study the shock Mach number (M) distribution as a function of pre-shock temperature, density, and redshift. Because of the large volume of the simulation, we have superb statistics that results from having thousands of galaxy clusters. We find that the Mach number evolution can be interpreted as a method to visualize large-scale structure formation. Shocks with Mach<5 typically trace mergers and complex flows, while 5<Mach<20 and Mach>20 generally follow accretion onto filaments and galaxy clusters, respectively. By applying results from nonlinear diffusive shock acceleration models using the first-order Fermi process, we calculate the amount of kinetic energy that is converted into cosmic ray protons. The acceleration of cosmic ray protons is large enough that in order to use galaxy clusters as cosmological probes, the dynamic response of the gas to the cosmic rays must be included in future numerical simulations.