Dynamics of stellar and HI streams in the Milky Way halo

S Jin

doi:10.1051/epjconf/20121902003

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 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.

Highlights

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. This is not a trivial task when faced with incomplete dynamical phase-space information, transverse motions of streams can be comprehended by harnessing the information contained within their radial velocity gradients
Such methods are applicable to stellar streams, and to HI streams residing in the Milky Way halo
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 140 kpc, showing that it may 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

Summary

INTRODUCTION

Stellar streams are ubiquitous in galaxy halos. are they observed in abundance within our own Milky Way galaxy, they are found to be teeming around the neighbouring Andromeda galaxy (PAndAS, [1]). The mounting evidence from these and other observations points to hierarchical growth and evolution of Milky Way-type galaxies through the continued assimilation of their satellite systems, sometimes long after the larger galaxies have settled down in their present-day form Referred to as ‘ultra-faint’ dwarf galaxies, some of these systems (Hercules, [4]; Ursa Major I, [5]; Ursa Major II, [6]) exhibit large ellipticities While they are not known to be embedded within stellar streams, their elongated forms beg the question of whether they might be experiencing Galactic tidal forces, or undergoing tidal disruption.

AN ORBIT FOR HERCULES

AN ORBITAL PATH FOR THE GCN STREAM

SUMMARY