Probing O vi Emission in the Halos of Edge‐on Spiral Galaxies

Abstract

We have used the Far Ultraviolet Spectroscopic Explorer to search for OVI 1031.926, 1037.617 A emission in the halos of the edge-on spiral galaxies NGC4631 and NGC891. In NGC4631, we detected OVI in emission toward a soft X-ray bubble above a region containing numerous Halpha arcs and filaments. The line-of-sight component of the motion of the OVI gas appears to match the underlying disk rotation. The observed OVI luminosities can account for 0.2-2% of the total energy input from supernovae (assuming a full OVI emitting halo) and yield mass flux cooling rates between 0.48 and 2.8 M_sun/yr 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 NGC891, a galaxy in a direction with considerably high foreground Galactic extinction.