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

Using GALAH (GALactic Archaeology with HERMES) survey data of nearby stars, we look
\nat how structure in the planar (u, v) velocity distribution depends on metallicity and on viewing
\ndirection within the Galaxy. In nearby stars with distance d  1 kpc, the Hercules stream is
\nmost strongly seen in higher metallicity stars [Fe/H] > 0.2. The Hercules stream peak v value
\ndepends on viewed galactic longitude, which we interpret as due to the gap between the stellar
\nstream and more circular orbits being associated with a specific angular momentum value of
\nabout 1640 km s−1 kpc. The association of the gap with a particular angular momentum value
\nsupports a bar resonant model for the Hercules stream. Moving groups previously identified
\nin Hipparcos (HIgh Precision Parallax COllecting Satellite) observations are easiest to see in
\nstars nearer than 250 pc, and their visibility and peak velocities in the velocity distributions
\ndepends on both viewing direction (galactic longitude and hemisphere) and metallicity. We
\ninfer that there is fine structure in local velocity distributions that varies over distances of a
\nfew hundred pc in the Galaxy.