Dynamics of stellar and HI streams in the Milky Way halo

Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany

^a e-mail: shoko@ari.uni-heidelberg.de

Abstract

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 Wayʼs 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 systemʼs orbit: for Hercules, one of the ‘ultra-faint’ dwarf galaxies exhibiting a large ellipticity and located at a distance of 140 kpc, 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 20 kpc.