The Hercules satellite: a stellar stream in the Milky Way halo?

Abstract

We investigate the possibility that the recently discovered Hercules Milky Way satellite is in fact a stellar stream in formation, thereby explaining its very elongated shape with an axis ratio of 3 to 1. Under the assumption that Hercules is a stellar stream and that its stars are flowing along the orbit of its progenitor, we find an orbit that would have recently brought the system close enough to the Milky Way to induce its disruption and transformation from a bound dwarf galaxy into a stellar stream. The application of simple analytical techniques to the tentative radial velocity gradient observed in the satellite provides tight constraints on the tangential velocity of the system (v_t = -16^{+6}_{-22} km/s in the Galactic Standard of Rest). Combined with its large receding velocity, the determined tangential velocity yields an orbit with a small pericentric distance (R_peri = 6^{+9}_{-2} kpc). Tidal disruption is therefore a valid scenario for explaining the extreme shape of Hercules. The increase in the mean flattening of dwarf galaxies as one considers fainter systems could therefore be the impact of a few of these satellites not being bound stellar systems dominated by dark matter but, in fact, stellar streams in formation, shedding their stars in the Milky Way's stellar halo.

8 pages, 4 figures, accepted for publication in ApJ

References in corpus (15)

• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from Kinematics of ~2400 SDSS Blue Horizontal Branch Stars
• Concentration, Spin and Shape of Dark Matter Haloes as a Function of the Cosmological Model: WMAP1, WMAP3 and WMAP5 results
• A common mass scale for satellite galaxies of the Milky Way
• Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function
• The Tidal Evolution of Local Group Dwarf Spheroidals
• The Highly Unusual Chemical Composition of the Hercules Dwarf Spheroidal Galaxy
• Modeling The Structure And Dynamics of Dwarf Spheroidal Galaxies with Dark Matter And Tides
• The origin of failed subhaloes and the common mass scale of the Milky Way satellite galaxies
• The Star Formation History and Extended Structure of the Hercules Milky Way Satellite
• The case for OH suppression at near-infrared wavelengths
• Is Ursa Major II the Progenitor of the Orphan Stream?
• GRB 060418 and 060607A: the medium surrounding the progenitor and the weak reverse shock emission
• A Suprime-Cam study of the stellar population of Ursa Major I dwarf spheroidal galaxy
• On the common mass scale of the Milky Way satellites

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