Metallicity Distribution of Disk Stars and the Formation History of the Milky Way

Abstract

We investigate the formation history of the stellar disk component in the Milky Way (MW) based on our new chemical evolution model. Our model considers several fundamental baryonic processes, including gas infall, re-accretion of outflowing gas, and radial migration of disk stars. Each of these baryonic processes in the disk evolution is characterized by model parameters, which are determined by fitting to various observational data of the stellar disk in the MW, including the radial dependence of the metallicity distribution function (MDF) of the disk stars, which has recently been derived in the APOGEE survey. We succeeded to obtain the best set of model parameters, which well reproduces the observed radial dependences of the mean, standard deviation, skewness, and kurtosis of the MDFs for the disk stars. We analyze the basic properties of our model results in detail to get new insights into the important baryonic processes in the formation history of the MW. One of the remarkable findings is that outflowing gas, containing much heavy elements, preferentially re-accretes onto the outer disk parts, and this recycling process of metal-enriched gas is a key ingredient to reproduce the observed narrower MDFs at larger radii. Moreover, important implications for the radial dependence of gas infall and the influence of radial migration on the MDFs are also inferred from our model calculation. Thus, the MDF of disk stars is a useful clue for studying the formation history of the MW.

Elemental abundances in the centre of the Galactic nuclear disc

“…Recent results presented by Toyouchi & Chiba (2018) show that their model predicts a metallicity [Fe/H] at the level of about +0.6 dex at a Galactocentric distance of 2 kpc (which is close to our observational result, see Andrievsky et al 2016). Unfortunately those authors did not study the chemical properties of the stellar disc component in the Milky Way Center.…”

The Canada–France Imaging Survey: Reconstructing the Milky Way Star Formation History from Its White Dwarf Population

“…This is followed by a roughly constant SFR to the present day. Our SFH matches the Toyouchi & Chiba (2018) results quite well at recent and ancient times but differs slightly at intermediate ages.…”

“…This result is also in line with the recent work by Mor et al (2019), who compared simulations of the Besançon Galactic model with the colors, magnitudes, and parallaxes from Gaia DR2, which shows a burst of star formation between 2 and 3 Gyr in the past. The slight bimodality suggested by Figure 11 is, however, not seen in the GCE models of Snaith et al (2014) andToyouchi &Chiba (2018), as seen in the right-hand panel of Figure 10.…”

“…In the right-hand panel of Figure 10, we compare our results to other SFHs found in the literature through GCE models. Toyouchi & Chiba (2018) used an openbox model, allowing for the inflow and outflow of gas, in order to reproduce the radial metallicity distribution obtained using APOGEE data in Hayden et al (2015). This result was obtained using a sample of red-giant stars with 3 < R < 15 kpc and |z| < 2 kpc, which is a much larger volume than our sample.…”

“…Also shown is the result ofRowell (2013), who inverted the white dwarf luminosity function ofHarris et al (2006) (green). Right: Comparing our star formation history to results obtained via Galactic chemical evolution models fromSnaith et al (2015) andToyouchi & Chiba (2018). Due to the varying units presented by each study, the SFHs have been normalized, and therefore only the shape should be compared.the SFR at 600 Myr is seen in the luminosity function of the local 40 pc white dwarf sample from Torres, & García-Berro…”