Unveiling the Intrinsic Alignment of Galaxies with Self-Calibration and
  DECaLS DR3 data
  Galaxy intrinsic alignment (IA) is both a source of systematic contamination
to cosmic shear measurement and its cosmological applications, and a source of
valuable information on the large scale structure of the universe and galaxy
formation. The self-calibration (SC) method \citep{SC2008} was designed to
separate IA from cosmic shear, free of IA modeling. It was first successfully
applied to the KiDS450 and KV450 data \citep{Yao2019}. We apply the SC method
to the DECaLS DR3 shear + photo-z catalog and significantly improve the IA
detection to $\sim 14\sigma$. We find a strong dependence of IA on galaxy
color, with strong IA signal ($\sim17.6\sigma$) for red galaxies, while the IA
signal for blue galaxies is consistent with zero. The detected IA for red
galaxies are in reasonable agreement with the non-linear tidal alignment model
and the inferred IA amplitude increases with redshift. We address the
systematics in the SC method carefully and performed several sanity checks. We
discuss various caveats and possible improvements in the measurement, theory
and parameter fitting that will be addressed in future works.
