Mapping the diffuse ultraviolet sky with the Galaxy Evolution Explorer

Abstract

We present a map of the diffuse ultraviolet cosmic background in two wavelength bands (FUV: 1530 Å and NUV: 2310 Å) over almost 75% of the sky using archival data from the Galaxy Evolution Explorer (GALEX) mission. Most of the diffuse flux is due to dust-scattered starlight and follows a cosecant law with slopes of 545 photons cm-2 s-1 sr -1 Å-1 and 433 photons cm-2 s -1 sr-1 Å-1 in the FUV and NUV bands, respectively. There is a strong correlation with the 100 μm Infrared Astronomy Satellite (IRAS) flux with an average UV/IR ratio of 300 photons cm-2 s-1 sr-1 Å-1 (MJy sr -1)-1 in the FUV band and that of 220 photons cm -2 s-1 sr-1 Å-1 (MJy sr -1)-1 in the NUV band but with significant variations over the sky. In addition to the large-scale distribution of the diffuse light, we note a number of individual features including bright spots around the hot stars Spica and Achernar. © 2010. The American Astronomical Society.