Properties of the Milky Way stellar disks in the direction of the Draco dSph galaxy

TL;DR

This study investigates the metallicity distribution and age of stars in the Milky Way's disks at different heights, revealing broader, more metal-rich distributions than standard models predict, and suggesting a revised thick disk structure.

Contribution

It provides new observational evidence on the metallicity and age distribution of Galactic disk stars, challenging standard models and proposing a smaller scale height for the thick disk.

Findings

Metallicity distributions are broader and more metal-rich than models predict.

Results support a smaller thick disk scale height and higher local normalization.

Existence of an intermediate age stellar population at 2 kpc above the Galactic plane.

Abstract

We present the first results of a study where we determine the metallicity distribution function in the Galactic disks as a function of height above the Galactic plane. Observations in the Stromgren photometric system enables us to identify the dwarf stars and derive metallicities for them. The resulting metallicity distribution functions at 0.5 and 2.0 kpc above the Galactic plane are significantly broader and more metal-rich than is anticipated from standard models such as the Besancon model. Our results can be explained by invoking a smaller scale height and larger local normalisation for the thick disk than is commonly used in the models. These results are compatible with recent determinations of the thick disk scale height based e.g. on SDSS data. The age of the stellar populations as a function of height above the Galactic plane is also investigated by studying the turn-off colour and metallicity. We tentatively find that at 2.0 kpc above the Galactic plane there exist an intermediate age population.