Investigating the two dust rings in the Andromeda galaxy

In 2006, observations of the Andromeda galaxy (M31) made by the Spitzer telescope (Barmby et
al., 2006) showed evidence of the presence of a ring-like system inside of its galactic disk (Block
et al., 2006). Even though the specific scenario of the creation of these two rings is still unclear,
numerical simulations made by Block et al. (2006) managed to reproduce them both, as well as their
characteristics (higher star formation rate in the outer ring, tilted inner ring,...) by investigating the
scenario of a collision between M31 and one of its companion galaxy, M32. The spatial resolution at
the time was however not sufficient to understand correctly the dynamics of the central kiloparsec.
This project thus aimed to reproduce the two rings by studying a collision between M31 and M32,
using a new generation of astrophysical code (ramses, Teyssier, 2002) which allows to have higher
resolution and better physical models.
We thus simulated a realistic, isolated and stable galaxy, possessing similar characteristics to those
of M31 such as two spiral arms, a stellar bar, or a similar rotation curve. The collision between this
galaxy and a single particle with a mass of 1/10th of M31’s and an initial velocity of 450 km/s was
then simulated. The results obtained showed the apparition of four successive rings in stars and gas
density, including the formation of a persistent inner ring when the impact parameter is non-zero.
However, the rings did not possess characteristics similar to what is found in the literature : we found
their radial velocities to go up to 27 km/s instead of the 14 km/s maximum (Block et al., 2006), a
ratio of 1/3 instead of 1/10 (Block et al., 2006) when comparing the radii between two consecutive
rings, and we did not find any tilt in the inner ring when a 43° tilt is observed in reality (Melchior
and Combes, 2011).