Determining The Galactic Halo's Emission Measure from UV and X-ray
  Observations
  We analyze a pair of Suzaku shadowing observations in order to determine the
X-ray spectrum of the Galaxy's gaseous halo. We simultaneously fit the spectra
with models having halo, local, and extragalactic components. The intrinsic
intensities of the halo OVII triplet and OVIII Lyman alpha emission lines are
9.98^{+1.10}_{-1.99} LU (line unit; photons cm^-2 s^-1 Sr^-1) and
2.66^{+0.37}_{-0.30} LU, respectively. Meanwhile, FUSE OVI observations for the
same directions and SPEAR CIV observations for a nearby direction indicate the
existence of hot halo gas at temperatures of ~10^{5.0} K to ~10^{6.0} K. This
collection of data implies that the hot gas in the Galactic halo is not
isothermal, but its temperature spans a relatively wide range from ~10^{5.0} K
to ~10^{7.0} K. We therefore construct a differential emission measure (DEM)
model for the halo's hot gas, consisting of two components. In each, dEM/dlog T
is assumed to follow a power-law function of the temperature and the gas is
assumed to be in collisional ionizational equilibrium. The low-temperature
component (LTC) of the broken power-law DEM model covers the temperature range
of 10^{4.80}-10^{6.02} K with a slope of 0.30 and the high-temperature
component (HTC) covers the temperature range of 10^{6.02}-10^{7.02} K with a
slope of -2.21. We find that a simple model in which hot gas accretes onto the
Galactic halo and cools radiatively cannot explain both the observed UV and
X-ray portions of our broken power-law model. It can, however, explain the
intensity in the Suzaku bandpass if the mass infall rate is 1.35*10^{-3} Msun
yr^-1 kpc^-2. The UV and X-ray intensities and our broken power-law model can
be well explained by hot gas produced by supernova explosions or by supernova
remnants supplemented by a smooth source of X-rays.
