Do the Electrons and Ions in X‐Ray Clusters Share the Same Temperature?

Abstract

The virialization shock around an X-ray cluster primarily heats the ions, since they carry most of the kinetic energy of the infalling gas. Subsequently, the ions share their thermal energy with the electrons through Coulomb collisions. We quantify the expected temperature di erence between the electrons and ions as a function of radius and time, based on a spherical self-similar model for the accretion of gas by a cluster in an ) \ 1, universe. Clusters with X-ray temperatures K show h 50 \ 1 T X \ 410 ] 107 noticeable di erences between their electron and ion temperatures at radii Mpc. High-resolution Z2 spectroscopy with future X-ray satellites such as Astro-E may be able to determine the ion temperature in intracluster gas from the width of its X-ray emission lines and compare it to the electron temperature as inferred from the free-free emission spectrum. Any di erence between these temperatures can be used to date the period of time that has passed since the infalling gas joined the cluster.