galaxies, homogeneity

In the morning, Jeremy Tinker (Berkeley) led our group meeting with a discussion of information about galaxy evolution from clustering. In the approximation that we know the dark matter model, the relationship between galaxies and dark matter can be parameterized and then the observed galaxy—galaxy clustering puts constraints on how the galaxies could possibly form and evolve. He has some counterintuitive results, from the fact that at intermediate redshift, the large-scale clustering of red and blue galaxies is very similar.

In the afternoon, Marc Kamionkowski (Caltech) gave the Big Apple Colloquium about the isotropy and homogeneity of large-scale structure, and in particular the cosmic microwave background. He is building non-natural models that permit anisotropy in the power spectrum while preserving isotropy in the temperature and density and all else. There is a small amount of evidence for this statistical anisotropy situation in the current data; it is a long shot but if it holds up it is extremely important.