Today was streams day at the Heidelberg–Oxford meetup. Sanders (Oxford) and Bovy showed their tidal-stream-modeling machineries, with emphases on the relationship between action-space and angle-space structure, or really frequency-space and angle-space structure. They both work only in integrable potentials, which creates one of the opportunities that Price-Whelan and I might exploit. That said, Sanders and Bovy have both developed some great computational simplicities that make their methods far faster than ours. For example, they can compute actions in any potential fast, angles pretty fast, and use affine approximations to local transformations to speed up integration over "true" phase-space positions. Bovy argued that Sanders's result from last year on streams not following orbits needs adjustment, when you consider the full frequency distribution hiding in every section of the stream. Sésar showed beautiful data on the Orphan Stream and advertised new work on RR Lyrae stars. He showed pretty convincingly that the Orphan Stream just ends abruptly at a location in which we could easily still observe it. Odd!
Schlafly (MPIA) and Sale (Oxford) showed work on three-dimensional dust mapping, which is essential both for understanding the stars and also for providing dust as a new tracer of the potential. Sales is working on non-parametrics with Gaussian Processes, like Bailer-Jones (MPIA) and Hanson (MPIA), while Schlafly is more old-school with independent angular pixels. That said, Schlafly has a complete map! We all emphasized the value for Schlafly of publishing not just the three-dimensional map, but also an easy-to-use tool for querying it.
Sormani (Oxford) made novel use of the "earth-mover distance" to compare features in images (models of the (l, v) distribution of gas in the Galactic Center and also data). The day ended with Martig (MPIA) showing beautiful galaxy simulations to investigate out-of-plane disk structure. It looks like the Monoceros-type stuff seen at the outskirts of the Milky Way might be quite typical.