Emission in the Halos of Edge - on Spiral Galaxies

We have used the Far Ultraviolet Spectroscopic Explorer to search for O VI λλ1031.926, 1037.617 emission in the halos of the edge-on spiral galaxies NGC 4631 and NGC 891. In NGC 4631, we detected O VI in emission toward a soft X-ray bubble above a region containing numerous Hα arcs and filaments. The line-of-sight component of the motion of the O VI gas appears to match the underlying disk rotation. The observed O VI luminosities can account for 0.2−2% of the total energy input from supernovae (assuming a full O VI emitting halo) and yield mass flux cooling rates between 0.48 and 2.8 M⊙ yr −1 depending on the model used in the derivations. Based on these findings, we believe it is likely that we are seeing cooling, galactic fountain gas. No emission was detected from the halo of NGC 891, a galaxy in a direction with considerably high foreground Galactic extinction.