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.
Highlights
The Milky Way (MW) offers the possibility of detailed observations of a large number of galactic properties, which are inaccessible in the case of other galaxies
The infall timescale of the disk as a function of radius is tailored to smoothly match the bulge timescale of τ(r < 2 kpc) ∼ 1.5 Gyr to the timescale of the outer disk while going through the value of τ(r = 8 kpc)∼7−8 Gyr for the solar neighbourhood. The latter has been shown to provide a good fit to the local metallicity distribution in simple models of the MW chemical evolution (e.g. Chiappini et al 1997; Boissier & Prantzos 1999) and we show that this is the case here (Sect. 4), the adopted
The data are split into thick disk and thin disk according to the prescription of Adibekyan et al (2013), in the middle panel of their Fig. 2
Summary
The Milky Way (MW) offers the possibility of detailed observations of a large number of galactic properties, which are inaccessible in the case of other galaxies. Roškar et al (2008) investigated the implications of radial migration for the chemical evolution of galactic disks with N-body+SPH simulations The main effects they found and analysed are: the resulting dispersion in the age-metallicity relation, the broadening of the local metallicity distribution, the flattening of observed past abundance profiles and the flattening of the observed past star formation history. We are inspired by N-body+SPH simulations – as in Minchev et al (2013) and Kubryk et al (2013) – and we adopt a parametrised description, using timeand radius-dependent diffusion coefficients In this way, we are able to quantitatively study the impact of epicyclic motion alone to the dispersion of the local age-metallicity relation and, the collective impact of the two processes (blurring+churning).
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