Tracing the Hercules stream around the Galaxy

Abstract

It has been proposed that the Hercules stream, a group of co-moving stars in the Solar neighborhood offset from the bulk of the velocity distribution, is the result of resonant interactions between stars in the outer disk and the Galactic bar. So far it has only been seen in the immediate Solar neighborhood, but the resonance model makes a prediction over a large fraction of the Galactic disk. I predict the distribution of stellar velocities and the changing Hercules feature in this distribution as a function of location in the Galactic disk in a simple model for the Galaxy and the bar that produces the observed Hercules stream. The Hercules feature is expected to be strong enough to be unambiguously detected in the distribution of line-of-sight velocities in selected directions. I identify quantitatively the most promising lines of sight for detection in line-of-sight velocities using the Kullback-Leibler divergence between the predictions of the resonance model and an axisymmetric model; these directions are at 250 deg <~ l <~ 290 deg. The predictions presented here are only weakly affected by distance uncertainties, assumptions about the distribution function in the stellar disk, and the details of the Galactic potential including the effect of spiral structure. Gaia and future spectroscopic surveys of the Galactic disk such as APOGEE and HERMES will be able to robustly test the origin of the Hercules stream and constrain the properties of the Galactic bar.

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Cited by in corpus (26)

• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• Extreme deconvolution: Inferring complete distribution functions from noisy, heterogeneous and incomplete observations
• Structure in phase space associated with spiral and bar density waves in an N-body galactic disk
• Revisiting the Tale of Hercules: how stars orbiting the Lagrange points visit the Sun
• The Galactic Disc in Action Space as seen by Gaia DR2
• Transient spiral structure and the disc velocity substructure in Gaia DR2
• Riding the kinematic waves in the Milky Way disk with Gaia
• Signatures of resonance and phase mixing in the Galactic disc
• The power spectrum of the Milky Way: Velocity fluctuations in the Galactic disk
• Tracing the Hercules stream with Gaia and LAMOST: new evidence for a fast bar in the Milky Way
• The 4:1 Outer Lindblad Resonance of a long slow bar as a potential explanation for the Hercules stream
• The LMC geometry and outer stellar populations from early DES data
• Spiral and bar driven peculiar velocities in Milky Way sized galaxy simulations
• Staying away from the bar: the local dynamical signature of slow and fast bars in the Milky Way
• On the stellar velocity distribution in the solar neighborhood in the light of Gaia DR2
• The Hercules stream as seen by APOGEE-2 South
• Vertical Oscillations of Fluid and Stellar Disks
• Combined dynamical effects of the bar and spiral arms in a Galaxy model. Application to the solar neighbourhood
• From ridges to manifolds: 3D characterization of the moving groups in the Milky Way disc
• Metallicity dependence of the Hercules stream in Gaia/RAVE data -- explanation by non-closed orbits
• Kinematics of Red Variables in the Solar Neighborhood I. Basic Data Obtained by an SiO Maser Survey
• Hercules and Wolf 630 Stellar Streams and Galactic Bar Kinematics
• The Aquarius Co-Moving Group is Not a Disrupted Classical Globular Cluster
• The GALAH Survey: Velocity fluctuations in the Milky Way using red clump giants
• Chemodynamical Ages of Small-Scale Kinematic Structures of the Galactic Disc in the Solar Neighborhood from ~250,000 K and M Dwarfs
• Collisionless Boltzmann equation approach for the study of stellar discs within barred galaxies