Metallicity Distribution of Disk Stars and the Formation History of the Milky Way

TL;DR

This study models the Milky Way's disk formation by fitting chemical evolution parameters to observed metallicity distributions, revealing key processes like gas re-accretion and radial migration shaping the galaxy's stellar composition.

Contribution

Introduces a comprehensive chemical evolution model that reproduces observed metallicity distributions and uncovers the significance of gas recycling and radial migration in MW formation.

Findings

Re-accretion of metal-rich gas influences outer disk MDFs.

Radial migration affects the skewness of MDFs.

Gas infall and recycling are crucial for disk evolution.

Abstract

We investigate the formation history of the stellar disk component in the Milky Way (MW) based on our new chemical evolution model. Our model considers several fundamental baryonic processes, including gas infall, re-accretion of outflowing gas, and radial migration of disk stars. Each of these baryonic processes in the disk evolution is characterized by model parameters, which are determined by fitting to various observational data of the stellar disk in the MW, including the radial dependence of the metallicity distribution function (MDF) of the disk stars, which has recently been derived in the APOGEE survey. We succeeded to obtain the best set of model parameters, which well reproduces the observed radial dependences of the mean, standard deviation, skewness, and kurtosis of the MDFs for the disk stars. We analyze the basic properties of our model results in detail to get new insights into the important baryonic processes in the formation history of the MW. One of the remarkable findings is that outflowing gas, containing much heavy elements, preferentially re-accretes onto the outer disk parts, and this recycling process of metal-enriched gas is a key ingredient to reproduce the observed narrower MDFs at larger radii. Moreover, important implications for the radial dependence of gas infall and the influence of radial migration on the MDFs are also inferred from our model calculation. Thus, the MDF of disk stars is a useful clue for studying the formation history of the MW.