The MW is an exceptionnally quiet galaxy: implications for spiral formation

We compare both the Milky Way and M31 to local external disk galaxies within the same mass range, using their relative locations in the planes formed by Vflat vs. MK (the Tully-Fisher relation), j_disk (specific angular momentum) and the average Fe abundance of stars in the galaxy outskirts. We find, for all relationships, that the MW is systematically offset by 1 sigma or more, showing a significant deficiency in stellar mass, angular momentum, disk radius and [Fe/H] in the stars in its outskirts at a given Vflat. Our Galaxy appears to have escaped any significant merger over the last 10-11 Gyr which may explain its peculiar properties. As with M31, most local spirals show evidence for a history shaped mainly by relatively recent merging.