G. Gilmore about "Population Models"

Gilmore reminds us that although previous speakers have talked about dry mergers and anti-hierarchical evolution, this certainly is not true for less massive systems. In addition, the secular evolution of bulges (pseudo-bulges) may not be the whole picture, since the Milky-way's (MW) pseudo-bulge has mainly old stars, as derived by their alpha-over-Fe ratio.

He goes on to talk about the main stellar populations: PopI in the thin disk, an intermediate Pop1.5 in the thick disk, PopII in the bulge and a not-yet detected PopIII of near-primordial stars. The thick disk is surprisingly homogeneous in element ratios which indicates a coherent build-up over a rather short timescale.

There is significant structure in the outer parts of the MW and recently several more streams are found around our galaxy, that origin from disrupted dwarf galaxies that are about to be "eaten up" and the model predictions for the different stellar populations are do not really match the observations.