We observed the edge-on spiral galaxy NGC 891 with the Position Sensitive Proportional Counter on ROSAT to search for hot extraplanar gas expected in the galactic fountain model. Diffuse X-ray emission surrounds the disk with a HWHM for the surface brightness perpendicular to the disk of 50" (2.4 kpc) and a radial extent of approximately 6.5 kpc, both of which are similar in extent to the extended Hα and radio halo component; the implied density scale height for the hot gas is 7 kpc. The spectrum is best fitted with a hard stellar component and a soft diffuse gas component of temperature 3.6 x 10^6^ K. The density of this gas is 2 x 10^-3^ cm^-3^, the luminosity is 4.4 x 10^39^ ergs s^-1^, the mass is 1 x 10^8^ M_sun_, and the pressure (P/k) is 1.4 x 10^4^ K cm^-3^. These data are consistent with this gas participating in a galactic fountain, where the material approaches hydrostatic equilibrium before cooling at a rate of 0.12 M_sun_ yr^-1^. The cooled material may be responsible for some of the Hα emission.
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Bregman et al. (1994) studied this question.