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

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 Coulombcollisions. We quantify the expected temperature difference between theelectrons and ions as a function of radius and time, based on a sphericalself-similar model for the accretion of gas by a cluster in an Omega=1, h=0.5universe. Clusters with X-ray temperatures T=(4-10)*10^7 K, show noticeabledifferences between their electron and ion temperatures at radii >2 Mpc. Highresolution spectroscopy with future X-ray satellites such as Astro E may beable to determine the ion temperature in intracluster gas from the width of itsX-ray emission lines, and compare it to the electron temperature as inferredfrom the free-free emission spectrum. Any difference between these temperaturescan be used to date the period of time that has passed since the infalling gasjoined the cluster.Comment: 18 pages, 3 figures, submitted to Ap