  A significant fraction of baryons in galaxies are in the form of diffuse gas
of the circumgalactic medium (CGM). One critical component of the multi-phases
of CGM, the so-called "coronal" warm-hot phase gas ($\rm 10^{5}-10^{6}$ K)
traced by O VI 1032, 1038 \r{A} resonance lines, has rarely been detected in
emission from galaxy halos other than Milky Way. Here we report four additional
detections of O VI emission gas in the halos of nearby edge-on galaxies, NGC
4631 and NGC 891, using archival Far Ultraviolet Spectroscopic Explorer data
and an updated data pipeline. We find the most intense O VI emission to be from
fields forming a vertical line near the center of NGC 4631, despite the close
proximity to the disk of two other fields. We theorize that the
vertically-oriented fields trace a warm-hot phase gas filament that is possibly
infalling onto the galaxy. The O VI kinematics of the fields closer to the
edges of the disk suggest that those fields sample ejected gas that has shock
heated and is cooling before returning to the disk. These results point to the
existence of filamentary structures of more intense O VI emission superimposed
within a more diffuse and faint O VI halo in star-forming galaxies.
Volume-filled O VI emission mapping is greatly needed to determine the
structure and prevalence of warm-hot gas and the role it plays in the cycling
of gas between the galaxy disk and the halo. Finally, we present the
sensitivity of future funded and proposed UV missions (LUVOIR-A, LUVOIR-B,
CETUS, and Aspera) to the detection of diffuse and faint O VI emission in
nearby galaxy halos.
