Dynamics of stellar and HI streams in the Milky Way halo

Stellar streams are key players in many aspects of Milky Way studies and, in particular, studying their orbital dynamics is crucial for furthering our understanding of the Milky Way's gravitational potential. Although this is not a trivial task when faced with incomplete dynamical phase-space information, transverse motions of streams can nevertheless be comprehended by harnessing the information contained within their radial velocity gradients. Such methods are not only applicable to stellar streams, but also to HI streams residing in the Milky Way halo. Here, I present the results of two studies that use radial velocity gradients to determine the system's orbit: for Hercules, one of the 'ultra-faint' dwarf galaxies exhibiting a large ellipticity and located at a distance of 140kpc, showing that it may in fact be a stellar stream, and for a string of high-velocity HI clouds belonging to the GCN complex, indicating its likelihood for being a gaseous stream at a distance of approximately 20kpc.Comment: 4 pages, 2 figures, to appear in the proceedings of "Assembling the Puzzle of the Milky Way", Le Grand-Bornand (Apr 17-22, 2011