stream search

Lauren Anderson (Flatiron) and Vasily Belokurov (Cambridge) have been developing a (relatively) model-free search for compact structures in phase-space, to be used on Gaia DR2 in April. Anderson showed me the current results, which highlight many possible streams, in pre-Gaia test data from SDSS (created by Sergey Koposov at CMU). She requires that the phase-space over-density be consistent with a section of a great circle, at a (somewhat) well-defined Galactocentric distance (because: reflex proper-motion from the Sun's velocity), moving in a direction along the circle. She finds lots of putative streams, but many of them seem to highlight edges and issues with the spatial selection function, so there are still issues to work out. The nice thing is that if we can get something working here, it will crush on the forthcoming Gaia data, which will have a much simpler selection function.