The Gaseous Halos of Galaxies as Revealed in X-ray Absorption

We propose the first systematic study of the extended Xray halos of normalgalaxies using absorption along the lineofsight to a carefullyselectedquasar. This observation will provide a fundamental test for models of galaxyformation by limiting the fraction of galaxy baryons associated with galaxyhalos. By constraining the extent and nature of these halos we will provideimportant constraints on solutions to the overcooling.. problem in galaxyformation and inform the missing baryon problem in cosmology. Our proposedexposure time will allow us to probe weak absorption lines down to the levelthat will for the first time provide meaningful constraints on the hot gascontent of galaxy halos. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]