Radial halo substructure in harmony with the Galactic bar

Abstract

Overdensities in the radial phase space $(r,v_r)$ of the Milky Way's halo have previously been associated with the phase-mixed debris of a highly radial merger event, such as Gaia Sausage-Enceladus. We present and test an alternative theory in which the overdense 'chevrons' are instead composed of stars trapped in resonances with the Galactic bar. We develop an analytic model of resonant orbits in the isochrone potential, and complement this with a test particle simulation of a stellar halo in a realistic barred Milky Way potential. These models are used to predict the appearance of action space $(J_{\varphi },J_r)$ and radial phase space in the Solar neighbourhood. They are able to reproduce almost all salient features of the observed chevrons. In particular, both the analytic model and simulation predict that the chevrons are more prominent at $v_r<0$ when viewed near the Sun, as is observed by Gaia. This is inconsistent with formation by an ancient merger event. We also associate individual chevrons with specific resonances. At a bar pattern speed of ${\Omega }_{\mathrm{b}}=35$ km s${}^{-1}$kpc${}^{-1}$, the two most prominent prograde chevrons align very closely with the corotation and outer Lindblad resonances. The former can be viewed as a highly eccentric extension of the Hercules stream. Finally, our model predicts that the $v_r$ asymmetry changes sign as a function of Galactic radius and azimuth, and we find evidence that this is indeed the case in the Milky Way.

arXiv comment20 pages, 18 figures, published in MNRAS

References in corpus (60)

• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• Local Kinematics and the Local Standard of Rest
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• The mass distribution and gravitational potential of the Milky Way
• Co-formation of the Galactic disc and the stellar halo
• Constraints from Dynamical Friction on the Dark Matter Content of Barred Galaxies
• AGAMA: Action-based galaxy modelling architecture
• The Effect of the Outer Lindblad Resonance of the Galactic Bar on the Local Stellar Velocity Distribution
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• 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
• Gaia Data Release 3 Properties and validation of the radial velocities
• Bar-Halo Interaction and Bar Growth
• Dynamical Friction and the Distribution of Dark Matter in Barred Galaxies
• The Milky Way stellar halo out to 40 kpc : Squashed, broken but smooth
• Substructure revealed by RR Lyraes in SDSS Stripe 82
• Bar-driven dark halo evolution: a resolution of the cusp--core controversy
• Order and chaos in the local disc stellar kinematics induced by the Galactic bar
• Contributions to the accreted stellar halo: an atlas of stellar deposition
• Parameters of 220 million stars from Gaia BP/RP spectra
• The pattern speed of the Milky Way bar from transverse velocities
• Origin and evolution of moving groups I. Characterization in the observational kinematic-age-metallicity space
• Revisiting the Tale of Hercules: how stars orbiting the Lagrange points visit the Sun
• The Milky Way Halo in Action Space
• Resonance sweeping by a decelerating Galactic bar
• Selecting accreted populations: metallicity, elemental abundances, and ages of the Gaia-Sausage-Enceladus and Sequoia populations
• Tree-ring structure of Galactic bar resonance
• A Recent Lindblad Resonance in the Solar Neighbourhood
• On the ridges, undulations & streams in Gaia DR2: Linking the topography of phase-space to the orbital structure of an N-body bar
• Resonances in Barred Galaxies
• Identifying resonances of the Galactic bar in Gaia DR2: I. Clues from action space
• Hic sunt dracones: Cartography of the Milky Way spiral arms and bar resonances with Gaia Data Release 2
• Trapped orbits and solar-neighbourhood kinematics
• The stellar mass distribution of the Milky Way's bar: an analytic model
• Stellar halo substructure generated by bar resonances
• Jeans modelling of the Milky Way's nuclear stellar disc
• Chemo-kinematics of the Milky Way spiral arms and bar resonances: connection to ridges and moving groups in the Solar vicinity
• Trojans in the Solar Neighborhood
• Energy wrinkles and phase-space folds of the last major merger
• Orbital tori for non-axisymmetric galaxies
• A skewer survey of the Galactic halo from deep CFHT and INT images
• Identifying resonances of the Galactic bar in Gaia DR2: II. Clues from angle space
• Resonant Trapping in the Galactic Disc and Halo and its Relation with Moving Groups
• Extending the Hyades
• The Gaia-ESO Survey: Dynamical models of flattened, rotating globular clusters
• RR Lyrae in XSTPS: The halo density profile in the North Galactic Cap
• Dark Matter Bars in Spinning Halos
• Chemodynamical signatures of bar resonances in the Galactic disk: current data and future prospects
• A 6-d View of Stellar Shells
• Effect of orbital trapping by bar resonances in the local U-V velocity field
• The Capture and Escape of Stars
• Ironing the folds: The phase space chevrons of a GSE-like merger as a dark matter subhalo detector
• Pattern speeds in the Milky Way
• The Debris of the "Last Major Merger" is Dynamically Young
• On the existence of a very metal-poor disc in the Milky Way

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• Observational Constraints of Radial Migration in the Galactic Disc Driven by the Slowing Bar
• $S^5$: New insights from deep spectroscopic observations of the tidal tails of the globular clusters NGC 1261 and NGC 1904
• Bar-driven dispersal of Galactic substructure
• How well can we unravel the accreted constituents of the Milky Way stellar halo? A test on cosmological hydrodynamical simulations
• A non-axisymmetric potential for the Milky Way disk
• Deciphering the Milky Way disc formation time encrypted in the bar chrono-kinematics
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data I. Method validation
• On the chaos induced by the Galactic bar on the orbits of nearby halo stars
• Dynamical streams in the local stellar halo
• First measurement of the triaxiality of the inner dark matter halo of the Milky Way
• GaiaUnlimited: The old stellar disc of the Milky Way as traced by the Red Clump
• Dynamical mirages: how bar-induced resonant trapping can mimic substructure clustering in dynamical parameter spaces
• The Pristine Survey -- XXVII. Journey to the Galactic outskirts -- Mapping the outer halo red giant stars down to the very metal-poor end
• Globular clusters in \textsc{OrbIT}: complete dynamical characterisation of the globular cluster population of the Milky Way through updated orbital reconstruction
• Dark matter spiral arms in Milky Way-like halos
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data III. Panoramic view of the bulge
• GSE vs. LMC: reshaping of radially biased stellar haloes by satellites
• Stirring Things Up: Bar-induced substructures in the stellar halo of a cosmological Milky Way analogue
• GalPort: Investigation of the bar in action-angle space