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 Coulomb collisions. We quantify the expected temperature difference 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 Omega=1, h=0.5 universe. Clusters with X-ray temperatures T=(4-10)*10^7 K, show noticeable differences between their electron and ion temperatures at radii >2 Mpc. High resolution 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 difference between these temperatures can be used to date the period of time that has passed since the infalling gas joined the cluster.Comment: 18 pages, 3 figures, submitted to Ap

Coding Geographic Areas Across Census Years: Creating Consistent Definitions of Metropolitan Areas

This paper presents suggested matches for the geographical coding (geocoding) of metropolitan areas in the 1970, 1980, and 1990 Censuses. The Census Bureau used different definitions and taxonomies to describe the geography of metropolitan areas in these three Census years. As a result, the geographical areas referred to by the standard Census Bureau definitions differ among the three Census data sets. The geographic matching scheme explained in this paper attempts to maximize consistency over time for metropolitan areas in the U.S.