Galactic Archaeology with asteroseismic ages. II. Confirmation of a delayed gas infall using Bayesian analysis based on MCMC methods

TL;DR

This study uses Bayesian MCMC methods to confirm a significant 4.5-5.5 Gyr delay between gas infall episodes in the Milky Way's disk, supporting the delayed gas-rich merger hypothesis in galactic evolution.

Contribution

First application of Bayesian MCMC analysis to constrain two-infall chemical evolution models with stellar ages and abundances, confirming a delayed gas infall in the Milky Way.

Findings

Delay between gas infall episodes is 4.5-5.5 Gyr.

Models reproduce multiple observational constraints.

Results support the delayed gas-rich merger scenario.

Abstract

With the wealth of information from large surveys and observational campaigns in the contemporary era, it is critical to properly exploit the data to constrain the parameters of Galactic chemical evolution models and quantify the associated uncertainties. We aim at constraining the two-infall chemical evolution models for the solar annulus using the measured chemical abundance ratios and seismically inferred age of stars in the APOKASC sample. In the revised two-infall chemical evolution models by Spitoni et al. (2019), a significant delay of $\sim 4.3$ Gyr has been invoked between the two episodes of gas accretion. In this work, we wish to test its robustness and statistically confirm/quantify the delay. For the first time, a Bayesian framework based on Markov Chain Monte Carlo methods has been used for fitting the two-infall chemical evolution models to the data. In addition to fitting the data for stars in the APOKASC sample, our best fit models also reproduce other important observational constraints of the chemical evolution of the disk: i) present day stellar surface density; ii) present day supernova and star formation rates; iii) the metallicity distribution function; and iv) solar abundance values. We found a significant delay between the two gas accretion episodes for various models explored with different values for the star formation efficiencies. The values for the delay lie in the range $4.5-5.5$ Gyr. The results suggest that the APOKASC sample carries the signature of delayed gas-rich merger, with the dilution as main process determining the shape of low-$\alpha$ stars in the abundance ratios space.