Universal properties of the high- and low-{\alpha} disk: small intrinsic abundance scatter and migrating stars

TL;DR

This study compares the age-abundance relations of stars in the high- and low-{\alpha} disks of the Milky Way, revealing universal element production and signatures of galaxy formation processes like inside-out growth and radial migration.

Contribution

It provides a detailed comparison of age-abundance relations across the Milky Way's disks and introduces a new age catalogue for APOGEE stars with improved age estimates.

Findings

Similar median intrinsic dispersions (~0.04 dex) in both disks suggest universal nucleosynthesis.

Shallower age-abundance relations in the high-{\alpha} disk indicate different formation histories.

Evidence of radial migration and inside-out formation patterns in the stellar distribution.

Abstract

The detailed age-chemical abundance relations of stars measures time-dependent chemical evolution.These trends offer strong empirical constraints on nucleosynthetic processes, as well as the homogeneityof star-forming gas. Characterizing chemical abundances of stars across the Milky Way over time has been made possible very recently, thanks to surveys like Gaia, APOGEE and Kepler. Studies of the low-${\alpha}$ disk have shown that individual elements have unique age-abundance trends and the intrinsic dispersion around these relations is small. In this study, we examine and compare the age distribution of stars across both the high and low-${\alpha}$ disk and quantify the intrinsic dispersion of 16 elements around their age-abundance relations at [Fe/H] = 0 using APOGEE DR16. We find the high-${\alpha}$ disk has shallower age-abundance relations compared to the low-${\alpha}$ disk, but similar median intrinsic dispersions of ~ 0.04 dex, suggesting universal element production mechanisms for the high and low-${\alpha}$ disks, despite differences in formation history. We visualize the temporal and spatial distribution of disk stars in small chemical cells, revealing signatures of upside-down and inside-out formation. Further,the metallicity skew and the [Fe/H]-age relations - across radius indicates different initial metallicity gradients and evidence for radial migration. Our study is accompanied by an age catalogue for 64,317 stars in APOGEE derived usingThe Cannon with ~ 1.9 Gyr uncertainty across all ages (APO-CAN stars) as well as a red clump catalogue of 22,031 stars with a contamination rate of 2.7%.