Chasing Accreted Structures within Gaia DR2 using Deep Learning

Abstract

In previous work, we developed a deep neural network classifier that only relies on phase-space information to obtain a catalog of accreted stars based on the second data release of Gaia (DR2). In this paper, we apply two clustering algorithms to identify velocity substructure within this catalog. We focus on the subset of stars with line-of-sight velocity measurements that fall in the range of Galactocentric radii $r\in [6.5,9.5]$ kpc and vertical distances $|z|<3$ kpc. Known structures such as Gaia Enceladus and the Helmi stream are identified. The largest previously-unknown structure, Nyx, is a vast stream consisting of at least 90 stars in the region of interest. This study displays the power of the machine learning approach by not only successfully identifying known features, but also discovering new kinematic structures that may shed light on the merger history of the Milky Way.

arXiv comment15 + 13 pages, 9 + 15 figures. v2: Minor changes in calculating probabilities to belong to a kinematic structure. Conclusions unchanged

References in corpus (83)

• emcee: The MCMC Hammer
• The NumPy array: a structure for efficient numerical computation
• Gaia Data Release 2. Summary of the contents and survey properties
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• galpy: A Python Library for Galactic Dynamics
• The Milky Way Tomography with SDSS: I. Stellar Number Density Distribution
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• SEGUE: A Spectroscopic Survey of 240,000 stars with g=14-20
• GIZMO: A New Class of Accurate, Mesh-Free Hydrodynamic Simulation Methods
• FIRE-2 Simulations: Physics versus Numerics in Galaxy Formation
• Tracing Galaxy Formation with Stellar Halos I: Methods
• Co-formation of the Galactic disc and the stellar halo
• The Radial Velocity Experiment (RAVE): first data release
• The GALAH Survey: Scientific Motivation
• Kinematics of Metal-Poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Non-Kinematically Selected Stars
• Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way
• Two Stellar Components in the Halo of the Milky Way
• Reconciling dwarf galaxies with LCDM cosmology: Simulating a realistic population of satellites around a Milky Way-mass galaxy
• Debris streams in the solar neighbourhood as relicts from the formation of the Milky Way
• Simulations of Galaxy Formation in a Lambda CDM Universe II: The Fine Structure of Simulated Galactic Disks
• Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics
• LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) The survey science plan
• The Radial Velocity Experiment (RAVE): Fifth Data Release
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars from SDSS DR7
• Detection of massive tidal tails around the globular cluster Pal 5 with SDSS commissioning data
• Great Circle tidal streams: evidence for a nearly spherical massive dark halo around the Milky Way
• Building up the Stellar Halo of the Galaxy
• Quantifying the Fragility of Galactic Disks in Minor Mergers
• Identification of A-colored Stars and Structure in the Halo of the Milky Way from SDSS Commissioning Data
• Detection of a 63 Degree Cold Stellar Stream in the Sloan Digital Sky Survey
• TeV Gamma Rays from Geminga and the Origin of the GeV Positron Excess
• Galaxia: a code to generate a synthetic survey of the Milky Way
• Fossil Signatures of Ancient Accretion Events in the Halo
• Cosmological simulations of the formation of the stellar haloes around disc galaxies
• Thin, thick and dark discs in LCDM
• A Prescription for Building the Milky Way's Halo from Disrupted Satellites
• The Disruption of the Sagittarius Dwarf Galaxy.
• The Milky Way's Stellar Disk
• Candidate RR Lyrae Stars Found in Sloan Digital Sky Survey Commissioning Data
• Lambda-Cold Dark Matter, Stellar Feedback, and the Galactic Halo Abundance Pattern
• Mapping the stellar structure of the Milky Way thick disk and halo using SEGUE photometry
• Mapping the substructure in the Galactic halo with the next generation of astrometric satellites
• The Sausage Globular Clusters
• Gaia Data Release 2: Properties and validation of the radial velocities
• Pieces of the puzzle: Ancient substructure in the Galactic disk
• One large blob and many streams frosting the nearby stellar halo in Gaia DR2
• The Case for the Dual Halo of the Milky Way
• Kinematics of SDSS subdwarfs: Structure and substructure of the Milky Way halo
• The Streams of the Gaping Abyss: A population of entangled stellar streams surrounding the Inner Galaxy
• Isochrone ages for ~3 million stars with the second Gaia data release
• Apocenter Pile-Up: Origin of the Stellar Halo Density Break
• The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage
• Characterization and history of the Helmi streams with Gaia DR2
• Phase-Space Distributions of Chemical Abundances in Milky Way-type Galaxy Halos
• Dark Matter Direct Detection Signals inferred from a Cosmological N-body Simulation with Baryons
• The Stellar Metallicity Distribution Function of the Galactic Halo from SDSS Photometry
• STREAMFINDER I: A New Algorithm for detecting Stellar Streams
• Synthetic Gaia surveys from the FIRE cosmological simulations of Milky Way-mass galaxies
• A box full of chocolates: The rich structure of the nearby stellar halo revealed by Gaia and RAVE
• Halo Substructure in the SDSS-Gaia Catalogue : Streams and Clumps
• A dark matter disc in three cosmological simulations of Milky Way mass galaxies
• Inferred Evidence For Dark Matter Kinematic Substructure with SDSS-Gaia
• Halo Star Streams in the Solar Neighborhood
• The Dark Disk of the Milky Way
• The Distribution of Dark Matter in the Milky Way's Disk
• The Halo's Ancient Metal-Rich Progenitor Revealed with BHB Stars
• Extended stellar systems in the solar neighborhood - II. Discovery of a nearby 120° stellar stream in Gaia DR2
• Insight Into the Formation of the Milky Way Through Cold Halo Substructure. I. The ECHOS of Milky Way Formation
• Halo streams in the 7th SDSS data release
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. II. A Chemodynamical Analysis
• Serendipitous Discovery of a Thin Stellar Stream near the Galactic Bulge in the Pan-STARRS1 3Pi Survey
• Under the Firelight: Stellar Tracers of the Local Dark Matter Velocity Distribution in the Milky Way
• Empirical Determination of Dark Matter Velocities using Metal-Poor Stars
• The Fractions of Inner- and Outer-Halo Stars in the Local Volume
• Identifying Stellar Streams in Gaia DR2 with Data Mining Techniques
• The dynamically selected stellar halo of the Galaxy with Gaia and the tilt of the velocity ellipsoid
• A Blueprint for the Milky Way's Stellar Populations: The Power of Large Photometric and Astrometric Surveys
• Insight Into the Formation of the Milky Way Through Cold Halo Substructure. III. Statistical Chemical Tagging in the Smooth Halo
• Insight Into the Formation of the Milky Way Through Cold Halo Substructure. II. The Elemental Abundances of ECHOS
• Cataloging Accreted Stars within Gaia DR2 using Deep Learning
• Leaves on trees: identifying halo stars with extreme gradient boosted trees

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• The Chemo-Dynamical Groups of Galactic Globular Clusters
• Reconstructing the Disrupted Dwarf Galaxy $Gaia$-Sausage/Enceladus Using its Stars and Globular Clusters
• Galactic Archaeology with Gaia
• Directional recoil detection
• Substructure in the stellar halo near the Sun. II. Characterisation of independent structures
• The kinematics of globular cluster populations in the E-MOSAICS simulations and their implications for the assembly history of the Milky Way
• Milky Way Accelerometry via Millisecond Pulsar Timing
• Substructure at High Speed II: The Local Escape Velocity and Milky Way Mass with Gaia DR2
• The stellar halo in Local Group Hestia simulations III. Chemical abundance relations for accreted and in-situ stars
• Dark matter substructures affect dark matter-electron scattering in xenon-based direct detection experiments
• Uncovering fossils of the distant Milky Way with UNIONS: NGC 5466 and its stellar stream
• The Milky Way, Coming into Focus: Precision Astrometry Probes its Evolution, and its Dark Matter
• Directional Detection of Dark Matter Using Solid-State Quantum Sensing
• Using Action Space Clustering to Constrain the Accretion History of Milky Way like Galaxies
• Robust Clustering of the Local Milky Way Stellar Kinematic Substructures with Gaia eDR3
• The Chemical Composition of Extreme-Velocity Stars
• Influence of the Gaia-Sausage-Enceladus on the density shape of the Galactic stellar halo revealed by halo K giants from the LAMOST survey
• Halo-independent bounds on the non-relativistic effective theory of WIMP-nucleon scattering from direct detection and neutrino observations
• Searching for Dwarf Galaxies in $Gaia$ DR2 Phase-Space Data Using Wavelet Transforms
• High-Resolution Chemical Abundances of the Nyx Stream
• Exploring the ex-situ components within Gaia DR3
• Substructure at High Speed I: Inferring the Escape Velocity in the Presence of Kinematic Substructure
• Halo-independent bounds on Inelastic Dark Matter
• Dynamical mirages: how bar-induced resonant trapping can mimic substructure clustering in dynamical parameter spaces
• Deciphering the Kinematic Substructure of Local Dark Matter with LAMOST K Giants
• Globular clusters in \textsc{OrbIT}: complete dynamical characterisation of the globular cluster population of the Milky Way through updated orbital reconstruction
• Applying machine learning to Galactic Archaeology: how well can we recover the origin of stars in Milky Way-like galaxies?
• Sensitivity of WIMP bounds on the velocity distribution in the limit of a massless mediator
• Dissecting stellar populations with manifold learning I. Validation of the method on a synthetic Milky Way-like galaxy
• Machine Learning for Galactic Archaeology: A chemistry-based neural network method for identification of accreted disc stars
• How to Build an Empirical Speed Distribution for Dark Matter in the Solar Neighborhood