On the Hot Gas Content of the Milky Way Halo
  The Milky Way appears to be missing baryons, as the observed mass in stars
and gas is well below the cosmic mean. One possibility is that a substantial
fraction of the Galaxy's baryons are embedded within an extended,
million-degree hot halo, an idea supported indirectly by observations of warm
gas clouds in the halo and gas-free dwarf spheroidal satellites. X-ray
observations have established that hot gas does exist in our Galaxy beyond the
local hot bubble; however, it may be distributed in a hot disk configuration.
Moreover, recent investigations into the X-ray constraints have suggested that
any Galactic corona must be insignificant. Here we re-examine the observational
data, particularly in the X-ray and radio bands, in order to determine whether
it is possible for a substantial fraction of the Galaxy's baryons to exist in ~
10^6 K gas. In agreement with past studies, we find that a baryonically closed
halo is clearly ruled out if one assumes that the hot corona is distributed
with a cuspy NFW profile. However, if the hot corona of the galaxy is in an
extended, low-density distribution with a large central core, as expected for
an adiabatic gas in hydrostatic equilibrium, then it may contain up to 10^11
M_sun of material, possibly accounting for all of the missing Galactic baryons.
We briefly discuss some potential avenues for discriminating between a massive,
extended hot halo and a local hot disk.
