On the Hot Gas Content of the Milky Way Halo. (arXiv:1211.0758v1 [astro-ph.CO])

On the Hot Gas Content of the Milky Way Halo. (arXiv:1211.0758v1 [astro-ph.CO]):
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.