GALEX observations of diffuse UV radiation at high spatial resolution from the Sandage Nebulosity

Abstract

We have observed a region of nebulosity first identified as starlight scattered by interstellar dust by Sandage using the Galaxy Evolution Explorer (GALEX) ultraviolet imaging telescope. Apart from airglow and zodiacal emission, we have found a diffuse UV background of between 500 and 800 photons cm/Sup–2 sr/Sup–1 s/Sup–1 Å/Sup–1 in both the GALEX far-ultraviolet (FUV) (1350-1750 Å) and NUV (1750-2850 Å) bands. Of this emission, up to 250 photons cm/Sup–2 sr/Sup–1 s/Sup–1 Å/Sup–1 is due to H/Sub2 fluorescent emission in the FUV band. The remainder is consistent with scattering from interstellar dust with forward scattering grains of albedo about 0.4. These are the highest spatial resolution observations of the diffuse UV background to date and show an intrinsic scatter beyond that expected from instrumental noise alone. Further modeling is required to understand the nature of this scatter and its implications for the ISM.