Tracing the Hercules stream with Gaia and LAMOST: new evidence for a fast bar in the Milky Way

Abstract

The length and pattern speed of the Milky Way bar are still controversial. Photometric and spectroscopic surveys of the inner Galaxy, as well as gas kinematics, favour a long and slowly rotating bar, with corotation around a Galactocentric radius of 6 kpc. On the other hand, the existence of the Hercules stream in local velocity space favours a short and fast bar with corotation around 4 kpc. This follows from the fact that the Hercules stream looks like a typical signature of the outer Lindblad resonance of the bar. As we showed recently, reconciling this local stream with a slow bar would need to find a yet unknown alternative explanation, based for instance on the effect of spiral arms. Here, by combining the TGAS catalogue of the Gaia DR1 with LAMOST radial velocities, we show that the position of Hercules in velocity space as a function of radius in the outer Galaxy indeed varies exactly as predicted by fast bar models with a pattern speed no less than 1.8 times the circular frequency at the Sun's position.

Accepted for publication in MNRAS Letters

References in corpus (9)

• The Radial Velocity Experiment (RAVE): first data release
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• The Structure of the Milky Way's Bar Outside the Bulge
• Made-to-Measure models of the Galactic Box/Peanut bulge: stellar and total mass in the bulge region
• The UK Met Office GCM with a sophisticated radiation scheme applied to the hot Jupiter HD 209458b
• The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
• The power spectrum of the Milky Way: Velocity fluctuations in the Galactic disk
• Staying away from the bar: the local dynamical signature of slow and fast bars in the Milky Way
• Tracing the Hercules stream around the Galaxy

Cited by in corpus (12)

• Revisiting long-standing puzzles of the Milky Way: the Sun and its vicinity as typical outer disk chemical evolution
• Trimodal structure of Hercules stream explained by originating from bar resonances
• Implications of a time-varying Galactic potential for determinations of the dynamical surface density
• The Hercules stream as seen by APOGEE-2 South
• Quantifying the (X/peanut)-shaped Structure of the Milky Way - New Constraints on the Bar Geometry
• Exploring the origin of moving groups and diagonal ridges by simulations of stellar orbits and birthplaces
• Distribution functions for resonantly trapped orbits in the Galactic disc
• Stars with fast Galactic rotation observed in Gaia TGAS: a signature driven by the Perseus arm?
• Effect of orbital trapping by bar resonances in the local U-V velocity field
• Impact of bar resonances in the velocity-space distribution of the solar neighbourhood stars in a self-consistent $N$-body Galactic disc simulation
• Gaia: the Galaxy in six (and more) dimensions
• Axial Asymmetry Studies in Gaia Data Release 2 Yield the Pattern Speed of the Galactic Bar