merger rates, stellar mass maps

Eric Bell (MPIA) pointed out in conversations about merger rates today that since the LRG mass function is very steep, there is a big difference between the merger rate considered as the probability that a given LRG will merge in the next Gyr and the probability that a given LRG had a major merger in its past. These differ because in the latter question you are dividing by the number of LRGs, and in the former you are dividing by the number of twice-as-massive LRGs. Of course Bell is interested in asking the latter question and we (Masjedi and I) are asking the former. I would say that we are asking the right question and Bell is asking the wrong one, because close pairs tell you about the future, not the past, but then again the evolution of the Universe is continuous, as I often argue.

James Pizagno (OSU) is also here visiting Rix, and we spent some time discussing the project of turning multi-wavelength images of galaxies, which show starlight, into stellar mass maps. Pizagno has some great code, and some very believable mass maps. In some spiral galaxies, the spiral arms disappear entirely when he goes from starlight to stellar mass. We agreed to test his code on some of my bright galaxies.