NGC 7457: Evidence for merger-driven cylindrical rotation in disc
  galaxies
  We construct Schwarzschild orbit-based models of NGC 7457, known as a
peculiar low-mass lenticular galaxy. Our best-fitting model successfully
retrieves most of the unusual kinematics behaviours of this galaxy, in which,
the orbital distribution of stars is dominated by warm and hot orbits. The
reconstructed surface brightness of the hot component matches fairly well the
photometric bulge and the reconstructed LOSVD map of this component shows clear
rotation around the major photometric axis of the galaxy. In the absence of a
dominant cold component, the outer part of our model is dominated by warm
orbits, representing an exponential thick disc. Our orbital analysis also
confirm the existence of a counter-rotating orbital substructure in the very
centre, reported in previous observational studies. By comparing our model with
a variety of simulation studies, and considering the stellar kinematics and
populations properties of this galaxy, we suggest that the thick disc is most
likely a dynamically heated structure, formed through the interactions and
accretion of satellite(s) with near-polar initial inclination. We also suggest
a merger-driven process as the most plausible scenario to explain the observed
and dynamically-modelled properties of the bulge of NGC 7457. We conclude that
both the high level of cylindrical rotation and unusually low velocity
dispersion reported for the NGC 7457 have most-likely external origins.
Therefore, NGC 7457 could be considered as a candidate for merger-driven
cylindrical rotation in the absence of a strong bar in disc galaxies.
