Non-Equilibrium Ionization State and Two-Temperature Structure in the Bullet Cluster 1E0657-56

TL;DR

This study uses simulations to explore non-equilibrium ionization and two-temperature structures in the Bullet cluster, revealing significant temperature differences and ionization state deviations that can be tested with future X-ray observations.

Contribution

It introduces detailed simulation analysis of non-equilibrium ionization and electron-ion temperature differences in a merging galaxy cluster, linking these effects to observable X-ray features.

Findings

Electron temperature varies significantly depending on thermal relaxation model.

Fe ionization states are out of equilibrium, affecting X-ray line ratios.

Results are testable with future high-energy X-ray observations.

Abstract

We investigate a non-equilibrium ionization state and an electron-ion two-temperature structure of the intracluster medium in the merging galaxy cluster, 1E0657-56 (the Bullet cluster), using a series of N-body and hydrodynamic simulations. We find that the electron temperature at the shock layer associated with the X-ray sub peak (bullet) is quite different depending on the thermal relaxation model between electrons and ions; ~25 keV for the Coulomb thermal relaxation model and ~45 keV for the instantaneous thermal relaxation model in the simulations which reproduce the observed X-ray morphology. Furthermore, both of Fe xxv and Fe xxvi are overabundant compared with the ionization equilibrium state around the shock layer, and thus, the intensity ratio between Fe xxv and Fe xxvi K alpha lines are significantly altered from that in the ionization equilibrium state. We also carry out the simulations with various sets of merger parameters, and discuss a possible range of the non-equilibrium effects in this system. Our results could be tested with future X-ray observations such as Astro-H with better sensitivity in high energy band.