The Flattening Metallicity Gradient in the Milky Way's Thin Disk

Abstract

We calculate the ages, orbits and phase-space coordinates for a sample of $\sim$4 million LAMOST and Gaia stars. The ages are crossmatched and compared with values from two other popular age catalogs which derive the ages using different methods. Of these $\sim$4 million stars, we select a sample of 1.3 million stars and investigate their radial metallicity gradients (as determined by orbital radii) as a function of their ages. This analysis is performed on various subsets of the data split by chemistry and orbital parameters. We find that commonly used selections for ``thin disk'' stars (such as low-$\alpha$ chemistry or vertically thin orbits) yield radial metallicity gradients which generally grow shallower for the oldest stars. We interpret this as a hallmark feature of radial migration (churning). Constraining our sample to very small orbital Z${}_{max}$ (the maximal height of a star's integrated orbit) makes this trend most pronounced. A chemistry-based ``thin disk'' selection of $\alpha$-poor stars displays the same trend, but to a lesser extent. Intruigingly, we find that ``thick disk'' selections in chemistry and Z${}_{max}$ reveal a slightly positive radial metallicity gradients which seem similar in magnitude at all ages. This may imply that the thick disk population is well mixed in age, but not in radius. This finding could help constrain conditions during the early epochs of Milky Way formation, and shed light on processes such as the accretion and reaccretion of gasses of different metallicities.

19 Pages, 13 Figures, Accepted to ApJ

References in corpus (22)

• The NumPy array: a structure for efficient numerical computation
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• The Dartmouth Stellar Evolution Database
• galpy: A Python Library for Galactic Dynamics
• The mass distribution and gravitational potential of the Milky Way
• New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey
• The GALAH Survey: Scientific Motivation
• Riding the Spiral Waves: Implications of Stellar Migration for the Properties of Galactic Disks
• Updated parameters of 1743 open clusters based on Gaia DR2
• Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
• Young [$\alpha$/Fe]-enhanced stars discovered by CoRoT and APOGEE: What is their origin?
• The age-metallicity structure of the Milky Way disk
• LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC): target selection and the first release of value-added catalogues
• Age velocity dispersion relations and heating histories in disc galaxies
• The effect of radial migration on galactic disks
• Ages and masses of million Galactic disk main sequence turn-off and sub-giant stars from the LAMOST Galactic spectroscopic surveys
• Origin of $\alpha$-rich young stars: clues from C, N and O
• Radial Migration from Metallicity Gradient of Open Clusters and Outliers
• Open Clusters as Tracers on Radial Migration of the Galactic Disk
• Local Stellar Kinematics from RAVE data - VII. Metallicity Gradients from Red Clump Stars
• Radial migration and vertical action in N-body simulations
• Metallicity Gradient of the Thick Disc Progenitor at High Redshift

Cited by in corpus (1)

• Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ($[Fe/H]\lesssim -3$) Regime