Detection of Ultraviolet Halos around Highly Inclined Galaxies
  We report the discovery of diffuse ultraviolet light around late-type
galaxies out to 5-20 kpc from the midplane using Swift and GALEX images. The
emission is consistent with the stellar outskirts in the early-type galaxies
but not in the late-type galaxies, where the emission is quite blue and
consistent with a reflection nebula powered by light escaping from the galaxy
and scattering off dust in the halo. Our results agree with expectations from
halo dust discovered in extinction by Menard et al. (2010) to within a few kpc
of the disk and imply a comparable amount of hot and cold gas in galaxy halos
(a few x 10^8 Msun within 20 kpc) if the dust resides primarily in Mg II
absorbers. The results also highlight the potential of UV photometry to study
individual galaxy halos.
