Queen's

I spent the day at Queen's University. After talking about Gaia-related matters, most of my time was spent with Larry Widrow and students or Stéphane Courteau and students.

Widrow's students are working on a lot of dynamical problems with disk galaxies and with n-body simulations. Three projects that stood out: His group can make disk galaxies that are (numerical) potential–density pairs and then evolve them forward in time or use them in galaxy–galaxy interaction simulations, even ones that are designed to fit real data. His group has revived (or made a new version of) the made to measure method as a new source of realistic galaxy models. And they are looking for tidal streams (or other phase-space structure) in n-body simulations; that is, treating the simulation outputs as data and searching it for structure.

Courteau's students are working on a range of precise measurements on nearby galaxies, including search for incredibly low surface-brightness structure in and around M31; building maps of the age and metallicity over the surfaces of extremely nearby galaxies, or as a function of radius in less nearby ones; and making much more precise the scaling relations that relate size, luminosity, and rotation velocity. In that latter project, his students do a large part of their radial profile fitting by hand—setting fitting ranges, choosing extrapolation techniques—which Courteau deems absolutely essential. Of course both my readers know how I feel about that! My take is this: If you want to do precise fitting of a simple model to a set of complex galaxies, you have to make a substantial number of choices, and somehow an extremely good student is far, far better than any currently available code for making those choices. Now fixing that is an important problem. That said, the scaling relations they get are amazingly precise.