Group-scale intrinsic galaxy alignments in the Illustris-TNG and
  MassiveBlack-II simulations
  We study the alignments of satellite galaxies, and their anisotropic
distribution, with respect to location and orientation of their host central
galaxy in MassiveBlack-II and IllustrisTNG simulations. We find that: the shape
of the satellite system in halos of mass ($> 10^{13}h^{-1}M_{\odot}$) is well
aligned with the shape of the central galaxy at $z=0.06$ with the mean
alignment between the major axes being $\sim \Delta \theta = 12^{\circ}$ when
compared to a uniform random distribution; that satellite galaxies tend to be
anisotropically distributed along the major axis of the central galaxy with a
stronger alignment in halos of higher mass or luminosity; and that the
satellite distribution is more anisotropic for central galaxies with lower star
formation rate, which are spheroidal, and for red central galaxies.Radially we
find that satellites tend to be distributed along the major axis of the shape
of the stellar component of central galaxies at smaller scales and the dark
matter component on larger scales. We find that the dependence of satellite
anisotropy on central galaxy properties and the radial distance is similar in
both the simulations with a larger amplitude in MassiveBlack-II. The
orientation of satellite galaxies tends to point toward the location of the
central galaxy at small scales and this correlation decreases with increasing
distance, and the amplitude of satellite alignment is higher in high mass
halos. However, the projected ellipticities do not exhibit a scale-dependent
radial alignment, as has been seen in some observational measurements.
