Matched photometric catalogs of GALEX UV sources with Gaia DR2 and SDSS
  DR14 databases (GUVmatch)
  We have matched the ultraviolet (UV) sources in GUVcat_AIS (Bianchi et
al.2017) with optical databases having similar depth and wide sky coverage.
GUVcat_AIS has GALEX far-UV (FUV, lambda-eff ~1528\AA ) and near-UV (NUV,
lambda-eff ~2310\AA) photometry of approx 83~million sources, covering 24,788
square degrees of the sky, with typical depth of FUV=19.9, NUV=20.8~ABmag.
Matches with Gaia and SDSS databases are presented here.
  Gaia data release 2 (DR2), covering the entire GUVcat footprint (Bianchi et
al. 2019), detected about one third of the $GUVcat\_AIS$ sources. We found
31,925,294 Gaia~DR2 counterparts to 30,024,791 GUVcat_AIS unique sources, with
photometry in $Gaia$~$G$ band, and often also in $Gaia$~$BP$ and $RP$ bands;
26,275,572 matches have a parallax measurement,
21,084,628/18,588,140/16,357,505 with parallax error less than 50%/30%/20%.
  The match with SDSS data release 14 (DR14) yields 23,310,532 counterparts to
22,207,563 unique GUVcat_AIS sources, 10,167,460 of which are point-like, over
a total overlap area of $\approx$11,100~square~degrees (Bianchi et al. 2019)}.
SDSS adds to the UV photometry five optical magnitudes: $u,g,r,i,z$, and
optical spectra of 860,224 matched sources.
  We used a match radius of 3arcsec, consistent with previous works (e.g.,
Bianchi et al. 2011a), although the positions agree to $\lesssim$1.5arcsec for
the majority of [point-like] matched-sources, in order to identify possible
multiple matches whose UV flux could be unresolved in GALEX imaging. The
catalogs can be trimmed to a tighter match radius using the provided
separation.
  The multi-band photometry is used to identify classes of astrophysical
objects that are prominent in UV, to characterise the content of the $GUVmatch$
catalogs, where stars in different evolutionary stages, QSOs, and galaxies can
be separated.
