Dark Matter and Metal Abundances in Elliptical Galaxies from X-ray   Observations of the Hot ISM
  I review the results of recent analysis and interpretation of X-ray observations of elliptical galaxies, focusing on elemental abundances and dark matter. The hot ISM is characterized by subsolar Fe abundances and solar Si-to-Fe ratios; and, I compare these with stellar abundances and discuss implications of these measurements. From models constructed to explain X-ray temperatures and their correlation with optical properties in a complete sample of ellipticals, I demonstrate the ubiquity of dark matter in bright elliptical galaxies, present limits on dark matter structural parameters, and discuss the scaling of dark halos with optical luminosity. The visual mass-to-light ratio within six optical effective radii has a universal value of 25 (for a Hubble constant of 80 km/sec/Mpc) that conflicts with the simplest extension of CDM theories of large scale structure formation to galactic scales. 
Michael Loewenstein (NASA/GSFC)