Chemodynamical evolution of the Milky Way disk

Abstract

In the first paper of this series (Paper I) we presented a new approach for studying the chemodynamical evolution in disk galaxies, focusing on the Milky Way. While in Paper I we studied extensively the Solar vicinity, here we extend these results to different distances from the Galactic center, looking for variations of observables that can be related to on-going and future spectroscopic surveys. By separating the effects of kinematic heating and radial migration, we show that migration is much more important, even for the oldest and hottest stellar population. The distributions of stellar birth guiding radii and final guiding radii (signifying contamination from migration and heating, respectively) widen with increasing distance from the Galactic center. As a result, the slope in the agemetallicity relation flattens significantly at Galactic radii larger than solar. We predict that the metallicity distributions of (unbiased) samples at different distances from the Galactic center peak at approximately the same value, [Fe/H] ≈ −0.15 dex, and have similar metal-poor tails extending to [Fe/H] ≈ −1.3 dex. In contrast, the metal-rich tail decreases with increasing radius, thus giving rise to the expected decline of mean metallicity with radius. Similarly, the [Mg/Fe] distribution always peaks at ≈0.15 dex, but its low-end tail is lost as radius increases, while the high-end diminishes at [Mg/Fe] ≈ 0.45 dex. The radial metallicity and [Mg/Fe] gradients in our model show significant variations with height above the plane because of changes in the mixture of stellar ages. An inversion in the radial metallicity gradient is found from negative to weakly positive (at r < 10 kpc), and from positive to negative for the [Mg/Fe] gradient, with increasing distance from the disk plane. We relate this to the combined effect of (i) the predominance of young stars close to the disk plane and old stars away from it; (ii) the more concentrated older stellar component; and (iii) the flaring of mono-age disk populations. We also investigate the effect of recycled gas flows on the mean [Fe/H] and find that in the region 4 < r < 12 kpc the introduced errors are less than 0.05-0.1 dex, related to the fact that inward and outward flows mostly cancel in that radial range. We show that radial migration cannot compete with the inside-out formation of the disk, exposed by the more centrally concentrated older disk populations, and consistent with recent observations.

Constraining the Milky Way assembly history with Galactic Archaeology

“…2 by Minchev et al 2016); -the age-[Fe/H] relation (Fig. 2 by Minchev et al 2016); -the flaring of mono-abundance populations (assuming similarity to mono-age populations) found by Bovy et al (2015) and predicted earlier by Minchev et al (2015), where Model 1 in the latter paper presents the same galaxy as the one used for the MCM13 chemodynamical model.…”

“…More detailed dynamical studies Minchev et al 2012a;Vera-Ciro et al 2014) have more recently shown that migration does not contribute to any significant level to disc thickening, but on the opposite, it suppresses flaring when external perturbations are included (Grand et al 2016;Minchev et al 2014a). This is discussed further in Sect.…”

“…Using data from the RAVE and SEGUE surveys, Minchev et al (2014b) presented a previously unknown chemokinematic relation, where the variation of stellar velocity dispersion with [Mg/Fe] ratios is reversed beyond 0.4 dex (Fig. 15, panel d).…”

“…In contrast to the isolated disc case, outward migrators cool the outer disc, thus working against disc flaring. Figure adapted from Minchev et al (2012a) and Minchev et al (2014a).…”

Galactic evolution of rapid neutron capture process abundances: the inhomogeneous approach

“…Recent chemodynamical galactic evolution models, like e.g., Minchev et al (2014), van de Voort et al (2015), and Shen et al (2015), can model in a self-consistent way massive mergers of galactic subsystems (causing effects like infall in simpler models), energy feedback from stellar explosions (causing effects like outflows), radial migrations in disk galaxies, mixing and diffusion of matter/ISM, and the initiation of star formation dependent on local conditions, resulting from the effects discussed above. In our present investigation we still utilize a more classical approach with a parametrized infall of primordial matter, and a Schmidt law (Schmidt 1959) for star formation.…”