The GALAH Survey: Stellar streams and how stellar velocity distributions vary with Galactic longitude, hemisphere and metallicity

Understand

Using GALAH survey data of nearby stars, we look at how structure in the planar (u,v) velocity distribution depends on metallicity and on viewing direction within the Galaxy.

• In nearby stars, with distance d < 1 kpc, the Hercules stream is most strongly seen in higher metallicity stars [Fe/H] > 0.2.
• The Hercules stream peak v value depends on viewed galactic longitude, which we interpret as due to the gap between the stellar stream and more circular orbits being associated with a specific angular momentum value of about 1640 km/s kpc.
• The association of the gap with a particular angular momentum value supports a bar resonant model for the Hercules stream.