The Age-Metallicity Relation in the Thin Disk of the Galaxy

TL;DR

This study analyzes the age-metallicity and Mg abundance relations in the Galaxy's thin disk using diverse data sources, revealing early low metallicity, decreasing dispersion, and a significant star formation increase around 4-5 billion years ago.

Contribution

It provides new insights into the chemical evolution and star formation history of the Galaxy's thin disk through comprehensive data analysis.

Findings

Metallicity dispersion decreased from 0.22 to 0.13 over time.

Mean metallicity increased around 4-5 billion years ago.

Star formation rate increased sharply about 4-5 billion years ago.

Abstract

HST trigonometric distances, photometric metallicities, isochronic ages from the second revised version of the Geneva--Copenhagen survey, and uniform spectroscopic Fe and Mg abundances from our master catalog are used to construct and analyze the age--metallicity and age-relative Mg abundance relations for stars of the thin disk. The influences of selection effects are discussed in detail. It is demonstrated that the radial migration of stars does not lead to appreciable distortions in the age dependence of the metallicity. During the first several billion years of the formation of the thin disk, the interstellar material in this disk was, on average, fairly rich in heavy elements (<[Fe/H]> ~-0.2) and poorly mixed. However, the metallicity dispersion continuously decreased with age, from \sigma_{[Fe/H]}~0.22 to ~0.13. All this time, the mean relative abundance of Mg was somewhat higher than the solar value (<[Mg/Fe]>~0.1). Roughly four to five billion years ago, the mean metallicity began to systematically increase, while retaining the same dispersion; the mean relative Mg abundance began to decrease immediately following this. The number of stars in this subsystem increased sharply at the same time. These properties suggest that the star-formation rate was low in the initial stage of formation of the thin disk, but abruptly increased about four to five billion years ago.