Andromeda: born out of a massive collision?

Was the Andromeda Galaxy, the largest and most massive galaxy in our local neighborhood, shaped into its current structure due to a monstrous collision over 6 billion years ago? According to a new study by some French astronomers, the answer is oui.
They created a lovely animation based on the model. It shows the collision of the two galaxies and how they interact:

Wow! You can see how the galaxies get disrupted, and perhaps get something of a feel for just how violent and incredible an event on this scale can be.
Using a sophisticated computer code that models the gravitational and fluid (pedantic: hydrodynamical) interaction between stars, gas, dust, and dark matter, they found that an ancient and massive collision between a galaxy a bit bigger than our Milky Way, and a smaller one about 1/3 the mass, reproduces a large amount of the structure we see in Andromeda today. That includes "…the large thin disk including its giant ring of gas and dust, the massive central bulge, the gigantic thick disk, the giant stream of old stars, as well as many other stellar streams discovered in the galaxy halo" according to the press release (the paper itself is ...