Hydrodynamic Simulations of Merging Galaxy Clusters: Non-Equilibrium
  Ionization State and Two-Temperature Structure
  We investigate a non-equilibrium ionization state and an electron-ion
two-temperature structure of the intracluster medium (ICM) in merging galaxy
clusters using a series of N-body and hydrodynamic simulations. Mergers with
various sets of mass ratios and impact parameters are systematically
investigated, and it is found that, in most cases, ICM significantly departs
from the ionization equilibrium state at the shock layers with a Mach number of
~1.5-2.0 in the outskirts of the clusters, and the shock layers with a Mach
number of ~2-4 in front of the ICM cores. Accordingly, the intensity ratio
between Fe xxv and Fe xxvi K alpha line emissions is significantly altered from
that in the ionization equilibrium state. If the effect of the two-temperature
structure of ICM is incorporated, the electron temperature is ~10-20 % and
~30-50 % lower than the mean temperature of ICM at the shock layers in the
outskirts and in front of the ICM cores, respectively, and the deviation from
the ionization equilibrium state becomes larger. We also address the dependence
of the intensity ratio on the viewing angle with respect to the merging plane.
