Dark Energy Survey Year 3 Results: Photometric Data Set for Cosmology
  We describe the Dark Energy Survey (DES) photometric data set assembled from
the first three years of science operations to support DES Year 3 cosmology
analyses, and provide usage notes aimed at the broad astrophysics community. Y3
Gold improves on previous releases from DES, Y1 Gold and Data Release 1 (DES
DR1), presenting an expanded and curated data set that incorporates algorithmic
developments in image detrending and processing, photometric calibration, and
object classification. Y3 Gold comprises nearly 5000 square degrees of grizY
imaging in the south Galactic cap, including nearly 390 million objects, with
depth reaching S/N ~ 10 for extended objects up to $i_{AB}\sim 23.0$, and
top-of-the-atmosphere photometric uniformity $< 3$ mmag. Compared to DR1,
photometric residuals with respect to Gaia are reduced by $50\%$, and
per-object chromatic corrections are introduced. Y3 Gold augments DES DR1 with
simultaneous fits to multi-epoch photometry for more robust galaxy color
measurements and corresponding photometric redshift estimates. Y3 Gold features
improved morphological star-galaxy classification with efficiency $>98\%$ and
purity $>99\%$ for galaxies with $19 < i_{AB} < 22.5$. Additionally, it
includes per-object quality information, and accompanying maps of the footprint
coverage, masked regions, imaging depth, survey conditions, and astrophysical
foregrounds that are used to select the cosmology analysis samples. This paper
will be complemented by online resources.
