Insights into the Formation and Evolution History of the Galactic Disk System

Abstract

We present a kinematic analysis of a sample of 23,908 G- and K-type dwarfs in the Galactic disk. Based on the $\alpha$-abundance ratio, [$\alpha$/Fe], we separated our sample into low-$\alpha$ thin-disk and high-$\alpha$ thick-disk stars. We find a $V_{\varphi }$ gradient of $-$28.2 km s${}^{-1}$ dex${}^{-1}$ over [Fe/H] for the thin disk, and an almost flat trend of the velocity dispersions of $V_{\mathrm{R}}$, $V_{\varphi }$, and $V_{\mathrm{Z}}$ components with [Fe/H]. The metal-poor (MP; [Fe/H] $<$ $-$0.3) thin-disk stars with low-$V_{\varphi }$ velocities have high eccentricities ($e$) and small perigalacticon distances ($r_{\mathrm{p}}$), while the high-$V_{\varphi }$ MP thin-disk stars possess low $e$ and large $r_{\mathrm{p}}$. Interestingly, half of the super metal-rich ([Fe/H] $>$ $+$0.1) stars in the thin disk exhibit low-$e$, solar-like orbits. Accounting for the inhomogeneous metallicity distribution of the thin-disk stars with various kinematics requires radial migration by churning $-$ it apparently strongly influences the current structure of the thin disk; we cannot rule out the importance of blurring for the high-$e$ stars. We derive a rotation velocity gradient of $+$36.9 km s${}^{-1}$ dex${}^{-1}$ for the thick disk, and decreasing trends of velocity dispersions with increasing [Fe/H]. The thick-disk population also has a broad distribution of eccentricity, and the number of high-$e$ stars increases with decreasing [Fe/H]. These kinematic behaviors could be the result of a violent mechanism, such as a gas-rich merger or the presence of giant turbulent clumps, early in the history of its formation. Dynamical heating by minor mergers and radial migration may also play roles in forming the current thick-disk structure.

arXiv comment17 pages, 12 figures, 3 tables, accepted for publication in ApJ

References in corpus (87)

• The Sloan Digital Sky Survey: Technical Summary
• Gaia Data Release 2. Summary of the contents and survey properties
• Gaia Data Release 2: The astrometric solution
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• 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
• Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood
• Radial Mixing in Galactic Discs
• Co-formation of the Galactic disc and the stellar halo
• The Radial Velocity Experiment (RAVE): first data release
• Elemental Abundance Survey of The Galactic Thick Disk
• The First Data Release (DR1) of the LAMOST general survey
• The GALAH Survey: Scientific Motivation
• Chemical evolution with radial mixing
• The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
• Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk
• Simulations of Galaxy Formation in a Lambda CDM Universe II: The Fine Structure of Simulated Galactic Disks
• The age structure of stellar populations in the solar vicinity. Clues of a two-phase formation history of the Milky Way disk
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• Chemodynamical evolution of the Milky Way disk I: The solar vicinity
• The Emergence of the Thick Disk in a CDM Universe
• The RAdial Velocity Experiment (RAVE): Fourth data release
• The thick disks of spiral galaxies as relics from gas-rich, turbulent, clumpy disks at high redshift
• The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters
• The Biggest Splash
• The Milky Way has no thick disk
• The Genesis of the Milky Way's Thick Disk via Stellar Migration
• The SEGUE Stellar Parameter Pipeline. III. Comparison with High-Resolution Spectroscopy of SDSS/SEGUE Field Stars
• Vertical distribution of Galactic disk stars I - Kinematics and metallicity
• The Gaia-ESO Survey: the Galactic Thick to Thin Disc transition
• Formation and Evolution of the Disk System of the Milky Way: [alpha/Fe] Ratios and Kinematics of the SEGUE G-Dwarf Sample
• Thin disc, Thick Disc and Halo in a Simulated Galaxy
• Chemodynamics of the Milky Way. I. The first year of APOGEE data
• The long lives of giant clumps and the birth of outflows in gas-rich galaxies at high redshift
• Galactic Archaeology with asteroseismic ages: evidence for delayed gas infall in the formation of the Milky Way disc
• A new alpha-enhanced super-solar metallicity population
• Radial Migration in Disk Galaxies I: Transient Spiral Structure and Dynamics
• Chemistry and Kinematics in the Solar Neighborhood: Implications for Stellar Populations and for Galaxy Evolution
• On the origin of the chemical bimodality of disk stars: A tale of merger and migration
• Constraining the thick disc formation scenario of the Milky Way
• Confirming chemical clocks: asteroseismic age dissection of the Milky Way disk(s)
• Kinematics and chemical properties of the Galactic stellar populations. The HARPS FGK dwarfs sample
• The SEGUE Stellar Parameter Pipeline. IV. Validation with an Extended Sample of Galactic Globular and Open Clusters
• The SEGUE Stellar Parameter Pipeline. V. Estimation of Alpha-Element Abundance Ratios From Low-Resolution SDSS/SEGUE Stellar Spectra
• Abundance to age ratios in the HARPS-GTO sample with Gaia DR2: Chemical clocks for a range of [Fe/H]
• The Gaia-ESO Survey: the chemical structure of the Galactic discs from the first internal data release
• Sausage & Mash: The dual origin of the Galactic thick disc and halo from the gas-rich Gaia-Enceladus-Sausage merger
• A spectroscopic survey of thick disc stars outside the solar neighbourhood
• The effect of radial migration on galactic disks
• The vertical motions of mono-abundance sub-populations in the Milky Way disk
• Orbital Eccentricity as a probe of Thick Disk Formation Scenarios
• Understanding inverse metallicity gradients in galactic discs as a consequence of inside-out formation
• Two Disk Components from a Gas Rich Disk-Disk Merger
• A new stellar chemo-kinematic relation reveals the merger history of the Milky Way disc
• The Rich Are Different: Evidence from the RAVE Survey for Stellar Radial Migration
• The HARPS search for southern extrasolar planets XXV. Results from the metal-poor sample
• The Metallicity Distribution Functions of SEGUE G and K dwarfs: Constraints for Disk Chemical Evolution and Formation
• Chemical gradients in the Milky Way from the RAVE data. I. Dwarf stars
• High-precision abundances of elements in Kepler LEGACY stars. Verification of trends with stellar age
• Modeling complete distributions with incomplete observations: The velocity ellipsoid from Hipparcos data
• Analysis of old very metal rich stars in the solar neighbourhood
• The GALAH Survey: Chemodynamics of the Solar Neighbourhood
• The 3D Velocity Structure of the Thick Disk from SPM4 and RAVE DR2
• Testing formation mechanisms of the Milky Way's thick disc with RAVE
• Evidence for the Third Stellar Population in the Milky Way's Disk
• The Gaia-ESO Survey: New constraints on the Galactic disc velocity dispersion and its chemical dependencies
• Impacts of a Flaring Star-forming Disc and Stellar Radial Mixing on the Vertical Metallicity Gradient
• Thick Disks in the Hubble Space Telescope Frontier Fields
• Chemical separation of disc components using RAVE
• Observational Evidence from SDSS for a Merger Origin of the Milky Way's Thick Disk
• Constraining churning and blurring in the Milky Way using large spectroscopic surveys -- an exploratory study
• Chemical and Kinematic Properties of the Galactic Disk from the LAMOST and Gaia Sample Stars
• The selection function of the RAVE survey
• The Gaia-ESO Survey: Churning through the Milky Way
• Detailed Analysis of Nearby Bulge-like Dwarf Stars I. Stellar Parameters, Kinematics and Oxygen Abundances
• The imprint of radial migration on the vertical structure of galaxy disks
• Effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way
• The thick disk rotation-metallicity correlation as a fossil of an "inverse chemical gradient" in the early Galaxy
• The selection function of the LAMOST Spectroscopic Survey of the Galactic Anticentre
• The Gaia-ESO Survey: Separating disk chemical substructures with cluster models
• Kinematics of the Galactic disk from LAMOST Dwarf sample
• Selection functions of large spectroscopic surveys
• Evidence of a large scale positive rotation-metallicity correlation in the Galactic thick disk

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• Galactic Dynamos
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• The nature of the Milky Way's stellar halo revealed by the three integrals of motion
• Chemodynamical Analysis of Metal-rich High-eccentricity Stars in the Milky Way's Disk
• The formation history of the Milky Way disc with high-resolution cosmological simulations
• Element abundance analysis of the metal-rich stellar halo and high-velocitythick disk in the galaxy