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ABSTRACT Stellar radial migration plays an important role in reshaping a galaxy’s structure and the radial distribution of stellar population properties. In this work, we revisit reported observational evidence for radial migration and quantify its strength using the age–[Fe/H] distribution of stars across the Milky Way with APOGEE data. We find a broken age–[Fe/H] relation in the Galactic disc at r > 6 kpc, with a more pronounced break at larger radii. To quantify the strength of radial migration, we assume stars born at each radius have a unique age and metallicity, and then decompose the metallicity distribution function (MDF) of mono-age young populations into different Gaussian components that originated from various birth radii at rbirth < 13 kpc. We find that, at ages of 2 and 3 Gyr, roughly half the stars were formed within 1 kpc of their present radius, and very few stars (<5 per cent) were formed more than 4 kpc away from their present radius. These results suggest limited short-distance radial migration and inefficient long-distance migration in the Milky Way during the last 3 Gyr. In the very outer disc beyond 15 kpc, the observed age–[Fe/H] distribution is consistent with the prediction of pure radial migration from smaller radii, suggesting a migration origin of the very outer disc. We also estimate intrinsic metallicity gradients at ages of 2 and 3 Gyr of −0.061 and −0.063 dex kpc−1, respectively.
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This content will become publicly available on July 31, 2026
A North–South Metallicity Asymmetry in the Outer Galactic Disk—Evidence for the Pericentric Passage of the Sagittarius Dwarf Galaxy
Abstract We present maps of the mean metallicity distributions on the GalactocentricR–Zplane at different azimuthal angles using red clump stars selected from the LAMOST and APOGEE surveys. In the inner disk (R < 11 kpc), the metallicity distribution is symmetric between the upper and lower disk. However, we find a north–south metallicity asymmetry in the outer disk (R > 11 kpc), especially toward the anti-Galactic center (−5∘ < Φ < 15°) direction. By further dissecting the map in age space, we detect this asymmetry across all mono-age stellar populations. However, the asymmetry is less pronounced in older populations (τ > 8 Gyr) compared to younger ones (τ < 6 Gyr). This reduced significance likely stems from three factors: larger age uncertainties, fewer stars in the outer disk, and the kinematically hotter nature of older populations. The observed metallicity asymmetry may be the consequence of the perturbation of the recent pericentric passage through the Galactic disk and tidal force of the well-known Sagittarius dwarf galaxy.
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- Award ID(s):
- 1927130
- PAR ID:
- 10649187
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 988
- Issue:
- 2
- ISSN:
- 2041-8205
- Page Range / eLocation ID:
- L70
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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