Today was day 4 of Galactic Archaeology and Stellar Physics. The day ended with my summary talk, which was unfair, scoldy, and mean and which was shouted (by me) over slides available here. Those slides will be incomprehensible without the things I said alongside them, but they will give you a sense of what themes I assembled (in real time) from the talks. A few non-representative highlights from today:
Binney kicked off the day with a discussion of analytic modeling of galaxies. His talk contained many valuable insights. For example, he showed that very simple distribution functions (in action space) can nonetheless create very non-trivial distributions in configuration space. He gave his usual—but excellent—argument for working in action–angle space: It is a consistent, continuous, conjugate coordinate system in which inference is possible. He also showed that high-quality modeling of the nearby Solar neighborhood can make good predictions for the position—velocity relationshiops for a larger patch of the Galaxy; that is, good modeling makes for highly predictive theories. At the end of his talk, he was asked about a radical dark-matter model, and he answered in terms of researcher utility, which was music to my ears.
Wegg showed an extremely good model of the mass function and microlensing optical depth towards the bulge, and constrained the dark-matter fraction. His results rule out a strong cusp in the dark matter, which is consistent with other things that were said at the meeting.
Grillmair and Carlberg talked about cold stellar streams. Grillmair showed marginal evidence for many more streams, consistent with a steep mass function in such objects. He name-checked our work on chaos and stream fanning. Carlberg shocked me by saying that the stellar streams are shorter than expected in theory. I just straight- up disagree with that, but maybe he is right when you take the full complement of streams together.
Côté brought us back to the subject of nucleosynthesis. He showed that there are many competing nucleosynthetic models that can produce the same data, but if you look on the inside, they imply very different things about the latent (physical) parameters. He breaks some of these by looking to LIGO and the rate of neutron-star mergers, which are probably involved in r-process. I loved the connections he drew between stellar chemical abundances, nuclear physics, and gravitational wave astronomy.