finding and characterizing halo streams in Gaia

Our weekly Gaia DR2 prep meeting once again got us into long arguments about substructure in the Milky Way halo, how to find it and how to characterize it. Wyn Evans (Cambridge) showed that when he looks at halo substructures he has found in terms of actions, they show larger spreads in action in some potentials and smaller in others. Will this lead to constraints on dynamics? Robyn Sanderson (Caltech) thinks so, and so did everyone in the room. Kathryn Johnston (Columbia) and I worked through some ideas for empirical or quasi-empirical stream finding in the data space, some of them inspired by the Schwarzschild-style modeling suggested by Sanderson in my office last Friday. And Lauren Anderson showed plots of Gaia expectations for substructure from simulations, visualized in the data space. We discussed many other things!

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