The impact of AGN feedback on galaxy intrinsic alignments in the Horizon
  simulations
  The intrinsic correlations of galaxy shapes and orientations across the
large-scale structure of the Universe are a known contaminant to weak
gravitational lensing. They are known to be dependent on galaxy properties,
such as their mass and morphologies. The complex interplay between alignments
and the physical processes that drive galaxy evolution remains vastly
unexplored. We assess the sensitivity of intrinsic alignments (shapes and
angular momenta) to Active Galactic Nuclei -AGN- feedback by comparing galaxy
alignment in twin runs of the cosmological hydrodynamical Horizon simulation,
which do and do not include AGN feedback respectively. We measure intrinsic
alignments in three dimensions and in projection at z=0 and z=1. We find that
the projected alignment signal of all galaxies with resolved shapes with
respect to the density field in the simulation is robust to AGN feedback, thus
giving similar predictions for contamination to weak lensing. The relative
alignment of galaxy shapes around galaxy positions is however significantly
impacted, especially when considering high-mass ellipsoids. Using a sample of
galaxy "twins" across simulations, we determine that AGN changes both the
galaxy selection and their actual alignments. Finally, we measure the
alignments of angular momenta of galaxies with their nearest filament. Overall,
these are more significant in the presence of AGN as a result of the higher
abundance of massive pressure-supported galaxies.
