The SDSS-IV eBOSS: emission line galaxy catalogues at z=0.8 and study of
  systematic errors in the angular clustering
  We present two wide-field catalogs of photometrically-selected emission line
galaxies (ELGs) at z=0.8 covering about 2800 deg^2 over the south galactic cap.
The catalogs were obtained using a Fisher discriminant technique described in a
companion paper. The two catalogs differ by the imaging used to define the
Fisher discriminant: the first catalog includes imaging from the Sloan Digital
Sky Survey and the Wide-Field Infrared Survey Explorer, the second also
includes information from the South Galactic Cap U-band Sky Survey (SCUSS).
Containing respectively 560,045 and 615,601 objects, they represent the largest
ELG catalogs available today and were designed for the ELG programme of the
extended Baryon Oscillation Spectroscopic Survey (eBOSS). We study potential
sources of systematic variation in the angular distribution of the selected
ELGs due to fluctuations of the observational parameters. We model the
influence of the observational parameters using a multivariate regression and
implement a weighting scheme that allows effective removal of all of the
systematic errors induced by the observational parameters. We show that
fluctuations in the imaging zero-points of the photometric bands have minor
impact on the angular distribution of objects in our catalogs. We compute the
angular clustering of both catalogs and show that our weighting procedure
effectively removes spurious clustering on large scales. We fit a model to the
small scale angular clustering, showing that the selections have similar biases
of 1.35/D_a(z) and 1.28/D_a(z). Both catalogs are publicly available.
