Wide-Field Lensing Mass Maps from DES Science Verification Data:
  Methodology and Detailed Analysis
  Weak gravitational lensing allows one to reconstruct the spatial distribution
of the projected mass density across the sky. These "mass maps" provide a
powerful tool for studying cosmology as they probe both luminous and dark
matter. In this paper, we present a weak lensing mass map reconstructed from
shear measurements in a 139 sq. deg area from the Dark Energy Survey (DES)
Science Verification (SV) data. We compare the distribution of mass with that
of the foreground distribution of galaxies and clusters. The overdensities in
the reconstructed map correlate well with the distribution of optically
detected clusters. We demonstrate that candidate superclusters and voids along
the line of sight can be identified, exploiting the tight scatter of the
cluster photometric redshifts. We cross-correlate the mass map with a
foreground magnitude-limited galaxy sample from the same data. Our measurement
gives results consistent with mock catalogs from N-body simulations that
include the primary sources of statistical uncertainties in the galaxy,
lensing, and photo-z catalogs. The statistical significance of the
cross-correlation is at the 6.8-sigma level with 20 arcminute smoothing. A
major goal of this study is to investigate systematic effects arising from a
variety of sources, including PSF and photo-z uncertainties. We make maps
derived from twenty variables that may characterize systematics and find the
principal components. We find that the contribution of systematics to the
lensing mass maps is generally within measurement uncertainties. In this work,
we analyze less than 3% of the final area that will be mapped by the DES; the
tools and analysis techniques developed in this paper can be applied to
forthcoming larger datasets from the survey.
