Kochfar & Silk on dry mergers

This week i'll present Kochfar & Silk, 'Dry Mergers: A crucial test for galaxy formation'
http://arxiv.org/abs/0809.1734

Abstract:
We investigate the role that dry mergers play in the build-up of massive galaxies within the cold dark matter paradigm. Implementing an empirical shut-off mass scale for star formation, we find a nearly constant dry merger rate of $ \sim 6 \times 10^{-5}$ Mpc$^{-3}$ Gyr$^{-1}$ at $z \leq 1$ and a steep decline at larger z. Less than half of these mergers are between two galaxies that are morphologically classified as early-types, and the other half is mostly between an early-type and late-type galaxy. Latter are prime candidates for the origin of tidal features around red elliptical galaxies. The introduction of a transition mass scale for star formation has a strong impact on the evolution of galaxies, allowing them only to grow by mergers above a characteristic mass scale of $M_{*,c} \sim 6.3 \times 10^{10}$ M$_{\odot}$. As a consequence of this transition, we find that around $M_{*,c}$, the fraction of 1:1 mergers is enhanced with respect to unequal mass major mergers. This suggest that it is possible to detect the existence of a transition mass scale by measuring the relative contribution of equal mass mergers to unequal mass mergers as a function of galaxy mass. The evolution of the high-mass end of the luminosity function is mainly driven by dry mergers at low z. We however find that only $10% -20%$ of galaxies more massive than $M_{*,c}$ experience dry major mergers within their last Gyr at $z \le 1$, and conclude that dry mergers do not significantly change the mass function at the high-mass end.

And if that's not exciting enough, there'll be donuts!