Bar-driven dispersal of Galactic substructure

Abstract

Galactic archaeologists often assume that integrals of motion (IoMs) such as $L_z$ and $E$ are conserved, so substructure remains frozen in IoM space over many Gyr. However, this is not true in the Milky Way due in part to its rotating bar. In this study we quantify the effects of the bar on the dynamics of substructure. We employ three different theoretical models: an analytical toy model; a set of test particle simulations with steady and slowing bars; and a cosmological zoom-in simulation of a Milky Way-like galaxy. Each model predicts that the bar increases the angular momentum and energy spread of low-energy substructures by a factor of $\sim 10-100$, so they cannot remain tightly clustered. We derive a criterion for determining when this effect is important. The most affected orbits are low energy ($E\lesssim E_{\odot }$, $r_{\mathrm{apo}}<40$ kpc), prograde, eccentric, or low inclination. This includes $\sim 3/4$ of Galactic globular clusters and $\sim 1/4$ of known stellar streams. We predict the presence of abundant bar-dispersed substructure. The structures remain much more tightly clustered in the space of metallicity and Jacobi integral $H_{\mathrm{J}}=E-{\Omega }_{\mathrm{b}}{L}_z$. We therefore propose using $H_{\mathrm{J}}$ and chemistry instead of traditional IoMs when searching for inner halo substructure. In $(L_z,E)$ space the dispersal of the structures is along a principal direction with gradient $\mathrm{d}E/\mathrm{d}{L}_z$ equal to the bar's pattern speed ${\Omega }_{\mathrm{b}}$. Bar-dispersed substructure should therefore allow the past evolution of ${\Omega }_{\mathrm{b}}$ to be constrained.

17 pages, 12 figures, published in MNRAS

References in corpus (54)

• Gaia Data Release 3: Summary of the content and survey properties
• E pur si muove: Galiliean-invariant cosmological hydrodynamical simulations on a moving mesh
• 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
• Radial Mixing in Galactic Discs
• Co-formation of the Galactic disc and the stellar halo
• The Auriga Project: the properties and formation mechanisms of disc galaxies across cosmic time
• AGAMA: Action-based galaxy modelling architecture
• A catalogue of masses, structural parameters and velocity dispersion profiles of 112 Milky Way globular clusters
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The Ages of 55 Globular Clusters as Determined Using an Improved delta V_TO^HB Method Along with Color-Magnitude Diagram Constraints, and Their Implications for Broader Issues
• Gaia EDR3 view on Galactic globular clusters
• Mean proper motions, space orbits and velocity dispersion profiles of Galactic globular clusters derived from Gaia DR2 data
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• Kraken reveals itself -- the merger history of the Milky Way reconstructed with the E-MOSAICS simulations
• "Skinny Milky Way, Please", says Sagittarius
• Life in the fast lane: a direct view of the dynamics, formation, and evolution of the Milky Way's bar
• From dawn till disk: Milky Way's turbulent youth revealed by the APOGEE+Gaia data
• Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy
• Chemodynamics of barred galaxies in cosmological simulations: On the Milky Way's quiescent merger history and in-situ bulge
• The pattern speed of the Milky Way bar from transverse velocities
• Robust Data-driven Metallicities for 175 Million Stars from Gaia XP Spectra
• The origin of galactic metal-rich stellar halo components with highly eccentric orbits
• The Poor Old Heart of the Milky Way
• Generation of mock tidal streams
• Resonance sweeping by a decelerating Galactic bar
• galstreams: A Library of Milky Way Stellar Stream Footprints and Tracks
• Dipping Our Toes in the Water: First Models of GD-1 as a Stream
• Action-based distribution functions for spheroidal galaxy components
• Tree-ring structure of Galactic bar resonance
• The Gaia DR3 view of dynamical substructure in the stellar halo near the Sun
• A direct measurement of the distance to the Galactic center using the kinematics of bar stars
• Nitrogen enrichment and clustered star formation at the dawn of the Galaxy
• Shepherding Tidal Debris with the Galactic Bar: The Ophiuchus Stream
• Trapped orbits and solar-neighbourhood kinematics
• Merger-induced galaxy transformations in the ARTEMIS simulations
• The stellar mass distribution of the Milky Way's bar: an analytic model
• The contribution of N-rich stars to the Galactic stellar halo using APOGEE red giants
• Stellar halo substructure generated by bar resonances
• Substructure in the stellar halo near the Sun. I. Data-driven clustering in Integrals of Motion space
• Milky Way total Mass derived by Rotation Curve and Globular Cluster kinematics from Gaia EDR3
• Testing kinematic distances under a realistic Galactic potential
• Measuring bar pattern speeds from single simulation snapshots
• Radial halo substructure in harmony with the Galactic bar
• The impact of a massive Sagittarius dSph on GD-1-like streams
• Separatrix Divergence of Stellar Streams in Galactic Potentials
• Observational Constraints of Radial Migration in the Galactic Disc Driven by the Slowing Bar
• Robust Clustering of the Local Milky Way Stellar Kinematic Substructures with Gaia eDR3
• Trojan globular clusters: radial migration via trapping in bar resonances
• A stellar census in globular clusters with MUSE. Metallicity spread and dispersion among first-population stars
• The ones that got away: chemical tagging of globular cluster-origin stars with Gaia BP/RP spectra
• Flipping of the tidal tails of the Ophiuchus stream due to the decelerating Galactic bar
• Dynamical streams in the local stellar halo
• Nearby stellar substructures in the Galactic halo from DESI Milky Way Survey Year 1 Data Release

Cited by in corpus (7)

• Dynamical mirages: how bar-induced resonant trapping can mimic substructure clustering in dynamical parameter spaces
• Globular clusters in \textsc{OrbIT}: complete dynamical characterisation of the globular cluster population of the Milky Way through updated orbital reconstruction
• Discovery of Galactic center ejected star in DESI DR1
• Stirring Things Up: Bar-induced substructures in the stellar halo of a cosmological Milky Way analogue
• Solar twins in Gaia DR3 GSP-Spec II. Age distribution and its implications for the Sun's migration
• Disentangling Milky Way halo populations at low metallicities using [Al/Fe]
• The chemodynamical memory of a major merger in a NIHAO-UHD Milky Way analogue -- I. A golden thread through time and space