R. Abraham: Morphology, the 6th road to downsizing

A very apt title, the topic of downsizing have been discussed in almost all of the talks in the galaxy session so far.

Five roads to downsizing: – Massive red and dead galaxies – Mass density evolution – Mass-segregated SFH – Abundant post starburst pop at z~1 – Evolutio of mass-metallicty relation

R.A. worry that this might be a “bandwagon” that everyone is jumping on. Galaxy evolution sweetspot is at z~1-2, highest derivative of mass assembly is at this time. Playing devil’s advocate he finds that if the z~0 points of mass essembly is correct, 50 % of massive galaxies are from between z~1-2. But this might be a problem of large errors in the derivations.

Use ACS observations of galaxy morpholgies at z~1-2 to investigate how the mass in stars have changed from 2 to 0. When doing this you have to make sure you’re going deep enough, that you have a sufficiently large area (should be larger than HDF) and to misapply the assymetry vs concentration diagram (S/N or completeness problems perhaps, not sure I got that, it could also be a question of which filters are used?).

How to measure morphology? R.A. thinks that concentration is not the best way to do this, rather use a more general statistic => Gini statistic/coefficient. This coefficient seems to be more robust than the concentration parameter. He finds that at z~1 about 70% of the stellar should exist in the early-type galaxies and that there is strong evolution in this fraction in z~1-2. Another conclusion is that mass density evolution of early types + assymetric early types is similar to the evolution of post-starbursts at z~3.