A Unified Exploration of the Chronology of the Galaxy

Abstract

The Milky Way has distinct structural stellar components linked to its formation and subsequent evolution, but disentangling them is nontrivial. With the recent availability of high-quality data for a large numbers of stars in the Milky Way, it is a natural next step for research in the evolution of the Galaxy to perform automated explorations with unsupervised methods of the structures hidden in the combination of large-scale spectroscopic, astrometric, and asteroseismic data sets. We determine precise stellar properties for 21,076 red giants, mainly spanning 2-15 kpc in Galactocentric radii, making it the largest sample of red giants with measured asteroseismic ages available to date. We explore the nature of different stellar structures in the Galactic disc by using Gaussian mixture models as an unsupervised clustering method to find substructure in the combined chemical, kinematic, and age subspace. The best-fit mixture model yields four distinct physical Galactic components in the stellar disc: the thin disc, the kinematically heated thin disc, the thick disc, and the stellar halo. We find hints of an age asymmetry between the Northern and Southern hemisphere and we measure the vertical and radial age gradient of the Galactic disc using the asteroseismic ages extended to further distances than previous studies.

arXiv comment18 pages, 12 figures, accepted for publication in MNRAS

References in corpus (96)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• 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
• Local Kinematics and the Local Standard of Rest
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• The K2 Mission: Characterization and Early results
• galpy: A Python Library for Galactic Dynamics
• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• A 3D Dust Map Based on Gaia, Pan-STARRS 1 and 2MASS
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• A Semi-Analytic Model for the Co-evolution of Galaxies, Black Holes, and Active Galactic Nuclei
• Kepler Mission Design, Realized Photometric Performance, and Early Science
• The New Galaxy: Signatures of its Formation
• Tracing Galaxy Formation with Stellar Halos I: Methods
• Co-formation of the Galactic disc and the stellar halo
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• The Chemical Evolution of the Galaxy: the two-infall model
• New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey
• A geometric distance measurement to the Galactic Center black hole with 0.3% uncertainty
• Star Formation and Feedback in Smoothed Particle Hydrodynamic Simulations--I. Isolated Galaxies
• The GALAH+ Survey: Third Data Release
• Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars
• The Auriga Project: the properties and formation mechanisms of disc galaxies across cosmic time
• 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
• Kepler Asteroseismology Program: Introduction and First Results
• Vertical waves in the solar neighbourhood in Gaia DR2
• Gaia Early Data Release 3 -- Catalogue validation
• Ages and fundamental properties of Kepler exoplanet host stars from asteroseismology
• Testing Scaling Relations for Solar-Like Oscillations from the Main Sequence to Red Giants using Kepler Data
• Streams, substructures and the early history of the Milky Way
• The Size Evolution of High Redshift Galaxies
• Asteroseismic fundamental properties of solar-type stars observed by the NASA Kepler Mission
• The Updated BaSTI Stellar Evolution Models and Isochrones: I. Solar Scaled Calculations
• Standing on the shoulders of Dwarfs: the Kepler asteroseismic LEGACY sample II - radii, masses, and ages
• The Biggest Splash
• Calculating asteroseismic diagrams for solar-like oscillations
• Actions for axisymmetric potentials
• The birth of the Milky Way as uncovered by accurate stellar ages with Gaia
• The Assembly of Milky Way-like Galaxies Since z~2.5
• Kraken reveals itself -- the merger history of the Milky Way reconstructed with the E-MOSAICS simulations
• Asteroseismic classification of stellar populations among 13000 red giants observed by Kepler
• The Galaxy-Halo Connection Over The Last 13.3 Gyrs
• Multiple retrograde substructures in the Galactic halo: A shattered view of Galactic history
• The underlying physical meaning of the ${\nu }_{\max }-{\nu }_{\mathrm{c}}$ relation
• The Payne: self-consistent ab initio fitting of stellar spectra
• Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy
• Mixed modes in red giants: a window on stellar evolution
• The Milky Way has no in-situ halo other than the heated thick disc. Composition of the stellar halo and age-dating the last significant merger with Gaia DR2 and APOGEE
• Galactic archaeology: mapping and dating stellar populations with asteroseismology of red-giant stars
• Abundance Estimates for 16 Elements in 6 Million Stars from LAMOST DR5 Low-Resolution Spectra
• Stellar population synthesis based modelling of the Milky Way using asteroseismology of 13000 Kepler red giants
• Galactic Archaeology with asteroseismic ages: evidence for delayed gas infall in the formation of the Milky Way disc
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• On the Formation of Galactic Thick Disks
• The age-metallicity structure of the Milky Way disk
• Age dissection of the Milky Way discs: red giants in the Kepler field
• Period spacings in red giants II. Automated measurement
• Giant star seismology
• Confirming chemical clocks: asteroseismic age dissection of the Milky Way disk(s)
• The solar neighbourhood age-metallicity relation - does it exist?
• Extreme deconvolution: Inferring complete distribution functions from noisy, heterogeneous and incomplete observations
• Measuring the vertical age structure of the Galactic disc using asteroseismology and SAGA
• Stellar Models with Enhanced Abundances of C, N, O, Ne, Na, Mg, Si, S, Ca, and Ti, in Turn, at Constant Helium and Iron Abundances
• Radial Mixing in Galactic Disks: The Effects of Disk Structure and Satellite Bombardment
• The First APOKASC Catalog of Kepler Dwarf and Subgiant Stars
• Chronologically dating the early assembly of the Milky Way
• Galactic Archaeology with asteroseismology and spectroscopy: Red giants observed by CoRoT and APOGEE
• Dissecting simulated disc galaxies II: the age-velocity relation
• A radial age gradient in the geometrically thick disk of the Milky Way
• Cannibals in the thick disk: the young $\alpha -$rich stars as evolved blue stragglers
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• Age-resolved chemistry of red giants in the solar neighbourhood
• Age dating of an early Milky Way merger via asteroseismology of the naked-eye star $\nu$ Indi
• The K2 Galactic Archaeology Program Data Release 1: Asteroseismic results from Campaign 1
• Changing the ${\nu }_{\max }$ Scaling Relation: The Need For a Mean Molecular Weight Term
• The K2 M67 Study: Revisiting old friends with K2 reveals oscillating red giants in the open cluster M67
• Deep Learning Classification in Asteroseismology
• The GALAH Survey: Chemodynamics of the Solar Neighbourhood
• A New Method for the Asteroseismic Determination of the Evolutionary State of Red-Giant Stars
• GRACES observations of young [alpha/Fe]-rich stars
• Characterizing epochs of star formation across the Milky Way disc using age-metallicity distributions of GALAH stars
• The Splash without a merger
• The tale of the tail -- disentangling the high transverse velocity stars in Gaia DR2
• Effective temperatures of red giants in the APOKASC catalogue and the mixing length calibration in stellar models
• The K2 Galactic Caps Project -- Going Beyond the \textit{Kepler} Field and Ageing the Galactic Disc
• Age-Dating Red Giant Stars Associated with Galactic Disk and Halo Substructures
• The K2 Galactic Archaeology Program Data Release 2: Asteroseismic results from campaigns 4, 6, & 7
• Filling the gaps: Gaussian mixture models from noisy, truncated or incomplete samples
• Star Formation Timescales of the Halo Populations from Asteroseismology and Chemical Abundances
• Partitioning the Galactic Halo with Gaussian Mixture Models
• The Galaxy and its stellar halo - insights from a hybrid cosmological approach

Cited by in corpus (6)

• The APO-K2 Catalog. II. Accurate Stellar Ages for Red Giant Branch Stars across the Milky Way
• Asteroseismic Study of Subgiants and Giants of the Open Cluster M67 using Kepler/K2: Expanded Sample and Precise Masses
• Exploring the dependence of chemical traits on metallicity: chemical trends for red giant stars with asteroseismic ages
• zoomies: A tool to infer stellar age from vertical action in Gaia data
• Asteroseismically Inferred Ages of 132,000 Red Giants with TESS
• Dissecting stellar populations with manifold learning I. Validation of the method on a synthetic Milky Way-like galaxy