Chemical enrichment and star formation in the Milky Way disk III. Chemodynamical constraints

TL;DR

This study analyzes the chemokinematical properties of Milky Way disk stars, revealing correlations between velocity dispersion and age, and discusses implications for disk evolution and star formation history.

Contribution

It provides new insights into the age-velocity dispersion relation and the use of orbital parameters as indicators of stellar birthplace, highlighting biases in current samples.

Findings

Velocity dispersion correlates with stellar age as t^0.26.

Vertex deviation does not strongly depend on stellar age.

Mean galactocentric radius is a reliable birthplace indicator.

Abstract

In this paper, we investigate some chemokinematical properties of the Milky Way disk, by using a sample composed by 424 late-type dwarfs. We show that the velocity dispersion of a stellar group correlates with the age of this group, according to a law proportional to t^0.26, where t is the age of the stellar group. The temporal evolution of the vertex deviation is considered in detail. It is shown that the vertex deviation does not seem to depend strongly on the age of the stellar group. Previous studies in the literature seem to not have found it due to the use of statistical ages for stellar groups, rather than individual ages. The possibility to use the orbital parameters of a star to derive information about its birthplace is investigated, and we show that the mean galactocentric radius is likely to be the most reliable stellar birthplace indicator. However, this information cannot be presently used to derive radial evolutionary constraints, due to an intrinsic bias present in all samples constructed from nearby stars. An extensive discussion of the secular and stochastic heating mechanisms commonly invoked to explain the age-velocity dispersion relation is presented. We suggest that the age-velocity dispersion relation could reflect the gradual decrease in the turbulent velocity dispersion from which disk stars form, a suggestion originally made by Tinsley and Larson (1978) and supported by several more recent disk evolution calculations. A test to distinguish between the two types of models using high-redshift galaxies is proposed.