Tidally induced morphology of M33 in hydrodynamical simulations of its
  recent interaction with M31
  We present a hydrodynamical model of M33 and its recent interaction with M31.
This scenario was previously proposed in the literature in order to explain the
distorted gaseous and stellar disks of M33, as well as the increased star
formation rate in both objects around 2 Gyr ago. We used an orbit integration
scheme to find which estimate of the transverse velocity of M31 more favors the
interaction scenario and then tried to reproduce it in our simulations. M33 was
modeled as a stellar and gaseous disk embedded in a live dark-matter halo,
while M31 was approximated only with a live dark halo. In the simulations the
two galaxies passed each other with a pericenter distance of 37 kpc. Tides
excited a two-armed spiral structure in the M33 disk, which is found to be the
predominant spiral signal in the observed galaxy and has been long known as a
feature easily induced by tidal interactions. We found that the gaseous warp
produced by the interaction did not resemble enough the observed one and we
performed an additional simulation including the hot gas halo of M31 to show
that this feature can be properly reproduced by tidal forces and ram pressure
stripping acting simultaneously on the gaseous disk. In addition to the spiral
arms, tidal forces produced the stellar stream similar to the observed one and
triggered a star formation burst at similar radii as it is observed.
