Simulating the Bullet Cluster

TL;DR

This paper uses high-resolution simulations to model the Bullet Cluster, reproducing observed features and exploring the impact of different initial conditions on the cluster's morphology and dynamics.

Contribution

It provides detailed N-body/SPH simulations of the Bullet Cluster, analyzing the effects of initial velocities, mass ratios, and dark matter concentration on observable features.

Findings

Observed X-ray and mass distribution features are well reproduced by specific collision parameters.

Higher dark matter concentration prevents disruption of the X-ray peak.

Dynamical friction causes the sub-cluster to remain bound at the end of the simulation.

Abstract

We present high resolution N-body/SPH simulations of the interacting cluster 1E0657-56. The main and the sub-cluster are modeled using extended cuspy LCDM dark matter halos and isothermal beta-profiles for the collisional component. The hot gas is initially in hydrostatic equilibrium inside the global potential of the clusters. We investigate the X-ray morphology and derive the most likely impact parameters, mass ratios and initial relative velocities. We find that the observed displacement between the X-ray peaks and the associated mass distribution, the morphology of the bow shock, the surface brightness and projected temperature profiles across the shock discontinuity can be well reproduced by offset 1:6 encounters where the sub-cluster has initial velocity (in the rest frame of the main cluster) close to 2 times the virial velocity of the main cluster dark matter halo. A model with the same mass ratio and lower velocity (1.5 times the main cluster virial velocity) matches quite well most of the observations. However, it does not reproduce the morphology of the main cluster peak. Dynamical friction strongly affects the kinematics of the sub-cluster so that the low velocity bullet is actually bound to the main system at the end of the simulation. We find that a relatively high concentration (c=6) of the main cluster dark matter halo is necessary in order to prevent the disruption of the associated X-ray peak. For a selected sub-sample of runs we perform a detailed three dimensional analysis following the past, present and future evolution of the interacting systems. In particular, we investigate the kinematics of the gas and dark matter components as well as the changes in the density profiles and the motion of the system in the L_X-T diagram.