Evolution of the Milky Way with radial motions of stars and gas I. The solar neighborhood and the thin and thick disk

TL;DR

This paper models the Milky Way's evolution, focusing on radial stellar and gas motions, to explain the properties of the thin and thick disks and their chemical evolution, using updated ingredients and simulations.

Contribution

It introduces a new model incorporating radial migration, gas flows, and updated yields, successfully reproducing observed properties of the Milky Way's disk and bulge.

Findings

Radial migration explains the properties of the thick and thin disks.

The thick disk has a shorter scale length (~1.8 kpc) than the thin disk.

Gas inflow velocity constrained to less than a few tenths of km/s.

Abstract

We study the role of radial migration of stars on the chemical evolution of the Milky Way disk. In particular, we are interested in the impact of that process on the local properties of the disk (age-metallicity relation and its dispersion, metallicity distribution, evolution of abundance ratios) and on the morphological properties of the resulting thick and thin disks.We use a model with several new or up-dated ingredients: atomic and molecular gas phases, star formation depending on molecular gas, yields from the recent homogeneous grid provided by Nomoto et al. (2013), observationally inferred SNIa rates. We describe radial migration with parametrised time- and radius-dependent diffusion coefficients, based on the analysis of a N-body+SPH simulation. We also consider parametrised radial gas flows, induced by the action of the Galactic bar. Our model reproduces well the present day values of most of the main global observables of the MW disk and bulge, and also the observed "stacked" evolution of MW-type galaxies from van Dokkum et al. (2013). The azimuthally averaged radial velocity of gas inflow is constrained to less than a few tenths of km/s. Radial migration is constrained by the observed dispersion in the age-metallicity relation. Assuming that the thick disk is the oldest (>9 Gyr) part of the disk, we find that the adopted radial migration scheme can reproduce quantitatively the main local properties of the thin and thick disk. The thick disk extends up to ~11 kpc and has a scale length of 1.8 kpc, considerably shorter than the thin disk, because of the inside-out formation scheme. We also show how, in this framework, current and forthcoming spectroscopic observations can constrain the nucleosynthesis yields of massive stars for the metallicity range of 0.1 solar to 2-3 solar.