Intrinsic alignments of disk and elliptical galaxies in the
  MassiveBlack-II and Illustris simulations
  We study the shapes and intrinsic alignments of disks and elliptical galaxies
in the MassiveBlack-II (MBII) and Illustris cosmological hydrodynamic
simulations, with volumes of $(100h^{-1}Mpc)^{3}$ and $(75h^{-1}Mpc)^{3}$
respectively. We find that simulated disk galaxies are more oblate in shape and
more misaligned with the shape of their host dark matter subhalo when compared
with ellipticals. The disk major axis is found to be oriented towards the
location of nearby elliptical galaxies. We also find that the disks are thinner
in MBII and misalignments with dark matter halo orientations are smaller in
both disks and ellipticals when compared with Illustris. As a result, the
intrinsic alignment correlation functions at fixed mass have a higher amplitude
in MBII than in Illustris. Finally, at scales above $\sim 0.1$\hmpc, the
intrinsic alignment two-point correlation functions for disk galaxies in both
simulations are consistent with a null detection, unlike those for ellipticals.
Despite significant differences in the treatments of hydrodynamics and baryonic
physics in the simulations, we find that the $w_{\delta +}$ correlation
function scales similarly with transverse separation. However, the less massive
galaxies show different scale dependence in the ED correlation. This result
indicates that, while hydrodynamic simulations are a promising tool to study
intrinsic alignments, further study is needed to understand the impact of
differences in the implementations of hydrodynamics and baryonic feedback.
