2018ApJ...864...34S

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 favors the interaction scenario more 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 long been 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 a stellar stream similar to the one observed and triggered a star formation burst at radii similar to where it is observed.