The Milky Way's Early Disk Was Built in Bursts. II. The Multi-component Age-Metallicity Structure of the High-α Disk
Abstract
Whether the high-α disk experienced a continuous or episodic star-formation history remains an open question. Here we investigate the age--metallicity distribution of the high-α disk using approximately 145,000 Gaia DR3 subgiants with [Fe/H]>−1, 6.5~kpc ≲ R≲9.5~kpc, and |Z|≲1.5~kpc. We adopt a forward-modelling framework that accounts for individual age and metallicity uncertainties and corrects for sample selection effects. The reconstructed distribution reveals two components: a broad, dominant population peaking at ∼10.6 Gyr and [Fe/H]≃−0.38, and an older, more metal-poor population peaking at ∼12.4 Gyr and [Fe/H]≃−0.79. These features suggest an episodic history of star formation and chemical enrichment in the high-α disk, qualitatively consistent with cosmological simulations in which recurrent gas accretion drives variations in the star formation rate. The age of the older component is close to the ∼12.3~Gyr epoch inferred for the proposed Low-energy--Kraken--Heracles accretion event, suggesting a possible connection between this early interaction and enhanced disk star formation. There is tentative evidence that the dominant population is possibly composed of two sub-components with age distributions peaking at ∼11.1 Gyr and ∼10.0 Gyr, respectively. Together, these results favour a picture in which the high-α disk was built through recurrent episodes of enhanced star formation rather than a single temporally smooth phase, even for the regime of [Fe/H]>−1.
Related
- From Dispersion to Metallicity: Probing the Milky Way Circumgalactic Medium with Fast Radio Bursts
- From the Milky Way to the Early Universe: How Metallicity Shapes the Formation of Double Neutron Stars
- The Milky Way’s Early Disk Was Built in Bursts. I. Evidence from Low-angular-momentum, High- α Stars Scattered Out of the Protodisk by Merger Events
- The Milky Way's Early Disk Was Built in Bursts. I. Evidence from Low-angular-momentum, High-α Stars Scattered Out of the Protodisk by Merger Events
- Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). VI. The age-metallicity relation of in situ clusters and the age of the Universe
BibTeX
@misc{sun2026milky,
title = {{The Milky Way's Early Disk Was Built in Bursts. II. The Multi-component Age-Metallicity Structure of the High-$α$ Disk}},
author = {Tiancheng Sun and Maosheng Xiang and Jifeng Liu and Meng Zhang and Yaqian Wu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.30659},
eprint = {2610.30659},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.30659},
}
RIS
TY - UNPB
TI - The Milky Way's Early Disk Was Built in Bursts. II. The Multi-component Age-Metallicity Structure of the High-α Disk
AU - Tiancheng Sun
AU - Maosheng Xiang
AU - Jifeng Liu
AU - Meng Zhang
AU - Yaqian Wu
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2610.30659
UR - https://arxiv.org/abs/2610.30659
AB - Whether the high-α disk experienced a continuous or episodic star-formation history remains an open question. Here we investigate the age--metallicity distribution of the high-α disk using approximately 145,000 Gaia DR3 subgiants with [Fe/H]>−1, 6.5~kpc ≲ R≲9.5~kpc, and |Z|≲1.5~kpc. We adopt a forward-modelling framework that accounts for individual age and metallicity uncertainties and corrects for sample selection effects. The reconstructed distribution reveals two components: a broad, dominant population peaking at ∼10.6 Gyr and [Fe/H]≃−0.38, and an older, more metal-poor population peaking at ∼12.4 Gyr and [Fe/H]≃−0.79. These features suggest an episodic history of star formation and chemical enrichment in the high-α disk, qualitatively consistent with cosmological simulations in which recurrent gas accretion drives variations in the star formation rate. The age of the older component is close to the ∼12.3~Gyr epoch inferred for the proposed Low-energy--Kraken--Heracles accretion event, suggesting a possible connection between this early interaction and enhanced disk star formation. There is tentative evidence that the dominant population is possibly composed of two sub-components with age distributions peaking at ∼11.1 Gyr and ∼10.0 Gyr, respectively. Together, these results favour a picture in which the high-α disk was built through recurrent episodes of enhanced star formation rather than a single temporally smooth phase, even for the regime of [Fe/H]>−1.
ER -