stream team

Kathryn Johnston and Marla Geha both brought their groups to NYU to discuss tidal streams in the Milky Way. Ana Bonaca showed the calibration process underway on her huge survey of the Palomar 5 stream. This globular cluster tidal stream extends for many tens of degrees in the SDSS imaging but then goes off the edge of the survey. Her DECam extend along the probable track. No results yet, but it is very exciting to see if the stream continues and what can be learned from it. Price-Whelan showed tantalizing evidence that, in a potential filled with chaotic orbits, tidal streams from progenitors on orbits with fast diffusion rates (short Lyapunov times) will produce streams with very different morphologies from those on orbits with slow diffiusion rates (long Lyapunov times). It is not yet clear how simple or general this is, but it is possible that chaos will be visible directly in streams and that the long streams we see are on especially (or unusually) non-chaotic orbits. That could explain things about alignments and so on. Emily Sandford (Columbia) is looking at better methods for identifying substructure interactions in the morphologies (including density distribution) of tidal streams. She is able to find energy gaps very reliably and is now looking at identifying the interactions in the simulation that produced them. The streams she has (which are from realistic n-body simulations) are really strange and unlike our standard observed streams; this might all relate to Price-Whelan's project!