Inferring the Morphology of Stellar Distribution in TNG50: Twisted and
  Twisted-Stretched shapes
  We investigate the morphology of the stellar distribution in a sample of
Milky Way (MW) like galaxies in the TNG50 simulation. Using a local in shell
iterative method (LSIM) as the main approach, we explicitly show evidence of
twisting (in about 52% of halos) and stretching (in 48% of them) in the real
space. This is matched with the re-orientation observed in the eigenvectors of
the inertia tensor and gives us a clear picture of having a re-oriented stellar
distribution. We make a comparison between the shape profile of dark matter
(DM) halo and stellar distribution and quite remarkably see that their radial
profiles are fairly close, especially at small galactocentric radii where the
stellar disk is located. This implies that the DM halo is somewhat aligned with
stars in response to the baryonic potential. The level of alignment mostly
decreases away from the center. We study the impact of substructures in the
orbital circularity parameter. It is demonstrated that in some cases, far away
substructures are counter-rotating compared with the central stars and may flip
the sign of total angular momentum and thus the orbital circularity parameter.
Truncating them above 150 kpc, however, retains the disky structure of the
galaxy as per initial selection. Including the impact of substructures in the
shape of stars, we explicitly show that their contribution is subdominant.
Overlaying our theoretical results to the observational constraints from
previous literature, we establish fair agreement.
