The Milky Way: An Exceptionally Quiet Galaxy; Implications for the formation of spiral galaxies

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Abstract
[Abridged]We compare both the Milky Way and M31 galaxies to local external disk galaxies within the same mass range, using their relative locations in the planes formed by V_flat versus M_K, j_disk, 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, showing a significant deficiency in stellar mass, in angular momentum, in disk radius and [Fe/H] in the stars in its outskirts at a given V_flat. On the basis of their location in the M_K, V_flat, and R_d volume, the fraction of spirals like the MW is 7+/-1%, while M31 appears to be a "typical'' spiral. Our Galaxy appears to have escaped any significant merger over the last ~10 Gyrs which may explain why it is deficient by a factor 2 to 3 in stellar mass, angular momentum and outskirts metallicity and then, unrepresentative of the typical spiral. As with M31, most local spirals show evidence for a history shaped mainly by relatively recent merging. We conclude that the standard scenario of secular evolution is generally unable to reproduce the properties of most (if not all) spiral galaxies. However, the so-called "spiral rebuilding'' scenario proposed by Hammer et al. 2005 is consistent with the properties of both distant galaxies and of their descendants - the local spirals.

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