Wechsler

[Yesterday:] Risa Wechsler (Chicago) gave a nice talk in which she showed that a simple insertion of galaxies into subhalos (dark-matter concentrations within virialized dark-matter halos) according to the subhalo circular velocity (expected velocity of a test particle on a circular orbit in the subhalo) produced a halo occupation (number of galaxies per halo of a given mass) that nicely explains the correlation function of galaxies and the abundance of galaxy groups of a fixed multiplicity. It also explained the variations in the correlation function with scale, galaxy luminosity, and even redshift.

This may all sound extremely technical, but (a) up till now the determination of halo occupation has been very ad-hoc and a posteriori, and (b) until we have simulations of enormous boxes in which the small-scale structure actually looks like the galaxies we actually see, low-resolution, large simulations plus halo occupation is the only way to reasonably model measurements that the community expects to use for the next five years of high-precision cosmology.

I also did the usual group-interacting and a small bit of referee-responding.