AREAcat: A Tool to Compute Area Coverage of GALEX UV GUVcat and BCScat, SDSS, PanSTARRS, and Gaia Source Catalogs in Chosen Sky Regions

We present AREAcat, an interactive online tool to compute the area mapped by recent catalogs that cover most of the sky, but not contiguously, such as the Galaxy Evolution Explorer (GALEX) ultraviolet (UV) source catalogs GUVcat_AIS. Constructed from 600 million measurements by removing duplicate measurements of the same source in repeated observations, and sources in field rims, GUVcat_AIS contains photometry in FUV (λeff ∼ 1528 ) and NUV (λeff ∼ 2310 ) of ∼83 million UV sources. When the surface density of a given class of objects is of interest, the actual area covered by the catalogs used in the source selection must be calculated, taking into account overlap among repeated observations and gaps between pointings. We developed a tool to calculate the area covered in any chosen region of the sky by GUVcat, as well as by the Sloan Digital Sky Survey data release 14 (SDSS DR14), the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) PS1 3π, Gaia DR2, and their overlap with GUVcat. The desired sky region can be specified in either Galactic (l, b) or equatorial ( , δ) coordinates. GUVcat flags sources within the footprint of extended objects, such as nearby large galaxies or Galactic stellar clusters, where the photometry of individual point-like sources is often compromised by crowding or by the underlying galaxy light. For statistical studies of clean samples over large areas, the sources within such extended objects can be excluded using the appropriate GUVcat flags; the corresponding regions can then be excised from the area estimate in AREAcat.