At the Astronomical Data group meeting and the Dynamics group meeting I spoke a bit about the Suroor Gandhi (NYU) project to make a sandbox to look at mixing of stellar populations in phase space. As I spoke about them, I realized that we might be able to infer a lot about the Milky Way from the Antoja spiral. For one, the overall aspect ratio of the spiral tells you something about the mass density in the disk (because that aspect ratio relates a distance to a velocity, and that will make an acceleration). For another, the pitch angle as a function of radius should tell you the scale height. And so on! This mirrors things Kathryn Johnston (Columbia) has been saying at me for a while, but I am a slow learner! The nice thing is that these projects might be possible even with extremely simplistic, toy simulations; some of the arguments are very general!
Side note: These arguments are very related to the project code-named Chemical Tangents that I have been talking about for a while: They are methods for just seeing the orbit structure at first order in the data. Unlike in, say, Jeans modeling or virial estimates, where the orbit structure only appears in second-order statistics.
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