Galaxies are surrounded by halos of hot gas whose mass and origin remain unknown .
One of the most challenging properties to measure is the metallicity , which constrains both of these .
We present a measurement of the metallicity around NGC 891 , a nearby , edge-on , Milky Way analog .
We find that the hot gas is dominated by low metallicity gas near the virial temperature at kT = 0.20 \pm 0.01 keV and Z / Z _ { \odot } = 0.14 \pm 0.03 ( stat ) ^ { +0.08 } _ { -0.02 } ( sys ) , and that this gas co-exists with hotter ( kT = 0.71 \pm 0.04 keV ) gas that is concentrated near the star-forming regions in the disk .
Model choices lead to differences of \Delta Z / Z _ { \odot } \sim 0.05 , and higher S / N observations would be limited by systematic error and plasma emission model or abundance ratio choices .
The low metallicity gas is consistent with the inner part of an extended halo accreted from the intergalactic medium , which has been modulated by star formation .
However , there is much more cold gas than hot gas around NGC 891 , which is difficult to explain in either the accretion or supernova-driven outflow scenarios .
We also find a diffuse nonthermal excess centered on the galactic center and extending to 5 kpc above the disk with a 0.3-10 keV L _ { X } = 3.1 \times 10 ^ { 39 } erg s ^ { -1 } .
This emission is inconsistent with inverse Compton scattering or single-population synchrotron emission , and its origin remains unclear .