The Ultraviolet Sky: An Overview from the GALEX Surveys
  The Galaxy Evolution Explorer (GALEX) has performed the first surveys of the
sky in the Ultraviolet (UV). Its legacy is an unprecedented database with more
than 200 million source measurements in far-UV (FUV) and near-UV (NUV), as well
as wide-field imaging of extended objects, filling an important gap in our view
of the sky across the electromagnetic spectrum. The UV surveys offer unique
sensitivity for identifying and studying selected classes of astrophysical
objects, both stellar and extra-galactic. We examine the overall content and
distribution of UV sources over the sky, and with magnitude and color. For this
purpose, we have constructed final catalogs of UV sources with homogeneous
quality, eliminating duplicate measurements of the same source. Such catalogs
can facilitate a variety of investigations on UV-selected samples, as well as
planning of observations with future missions.
  We describe the criteria used to build the catalogs, their coverage and
completeness. We included observations in which both the far-UV and near-UV
detectors were exposed; 28,707 fields from the All-Sky Imaging survey (AIS)
cover a unique area of 22,080 square degrees (after we restrict the catalogs to
the central 1-degree diameter of the field), with a typical depth of about
20/21 mag (FUV/NUV, in the AB mag system), and 3,008 fields from the
Medium-depth Imaging Survey (MIS) cover a total of 2,251 square degrees at a
depth of about 22.7mag. The catalogs contain about 71 and 16.6 million sources
respectively. The density of hot stars reflects the Galactic structure, and the
number counts of both Galactic and extra-galactic sources are modulated by the
Milky Way dust extinction, to which the UV data are very sensitive.
