Non-Equilibrium Ionization State and Two-Temperature Structure in the Linked Region of Abell 399 and Abell 401

Abstract

We investigate a non-equilibrium ionization state and a two-temperature structure of the intracluster medium in the linked region of Abell 399 and Abell 401, using a series of |$N$|-body |$+$| Smoothed Particle Hydrodynamics (SPH) simulations, and find that there exist significant shock layers at the edge of the linked region and that the ionization state of iron departs from the ionization equilibrium state at the shock layers and around the center of the linked region. As for the two-temperature structure, an obvious difference in temperature between electrons and ions is found in the edge of the linked region. The K|$\alpha$| line emissions of Fe xxiv and Fe xxv are not severely affected by the deviation from the ionization equilibrium state around the center of the linked region, suggesting that the detection of relatively high metallicity in this area cannot be ascribed to a non-equilibrium ionization state of the intracluster medium. On the other hand, the K|$\alpha$| emissions significantly deviate from the equilibrium values at the shock layers, and the intensity ratio of the K|$\alpha$| lines between Fe xxiv–xxv and Fe xxvi is found to be significantly different from that in the ionization equilibrium state.