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

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Cited by in corpus (32)

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• Trapped orbits and solar-neighbourhood kinematics
• Chemo-kinematics of the Milky Way spiral arms and bar resonances: connection to ridges and moving groups in the Solar vicinity
• 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
• Galactic Bar Resonances Inferred from Kinematically Hot Stars in Gaia EDR3
• The Hercules stream as seen by APOGEE-2 South
• Identifying resonances of the Galactic bar in Gaia DR2: II. Clues from angle space
• 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
• Tracing Hercules in Galactic azimuth with Gaia DR2
• Distribution functions for resonantly trapped orbits in the Galactic disc
• The bar resonances and low angular momentum moving groups in the Galaxy revealed by stellar ages
• Moving groups across Galactocentric radius with Gaia DR3
• On the Chemical and Kinematic Consistency Between N-rich Metal-poor Field Stars and Enriched Populations in Globular Clusters
• Angle-action variables for orbits trapped at a Lindblad resonance
• Disentangling the Arcturus stream
• 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
• Frequencies, chaos and resonances: a study of orbital parameters of nearby thick disc and halo stars
• Impact of bar resonances in the velocity-space distribution of the solar neighbourhood stars in a self-consistent $N$-body Galactic disc simulation
• Spatial and velocity offsets of Galactic masers from the centers of spiral arms
• Five methods for determining pattern speeds in galaxies
• Radial and azimuthal gradients of the moving groups in Gaia DR3: The slow/fast bar degeneracy problem
• On the Migration Origin of the Hercules Moving Group with GAIA, LAMOST, APOGEE, and GALAH Surveys
• Gaia: the Galaxy in six (and more) dimensions
• Axial Asymmetry Studies in Gaia Data Release 2 Yield the Pattern Speed of the Galactic Bar
• On the origin of the Hercules group: I. chemical signatures indicating the outer bar origin
• Resonant Effects of a Bar on the Galactic Disk Kinematics Perpendicular to Its Plane
• Moving Groups in the Solar Neighborhood with Gaia, APOGEE, GALAH, and LAMOST: Dynamical Effects Gather Gas and the Ensuing Star Formation Plays an Important Role in Shaping the Stellar Velocity Distributions