APOGEE DR16: A multi-zone chemical evolution model for the Galactic disc based on MCMC methods

Spitoni, E.; Verma, K.; Silva Aguirre, V.; Vincenzo, F.; Matteucci, F.; Vaičekauskaitė, B.; Palla, M.; Grisoni, V.; Calura, F.

Abstract

Context. The analysis of the latest release of the Apache Point Observatory Galactic Evolution Experiment project (APOGEE DR16) data suggests the existence of a clear distinction between two sequences of disc stars at different Galactocentric distances in the [α/Fe] versus [Fe/H] abundance ratio space: the so-called high-α sequence, classically associated with an old population of stars in the thick disc with high average [α/Fe], and the low-α sequence, which mostly comprises relatively young stars in the thin disc with low average [α/Fe].

Aims. We aim to constrain a multi-zone two-infall chemical evolution model designed for regions at different Galactocentric distances using measured chemical abundances from the APOGEE DR16 sample.

Methods. We performed a Bayesian analysis based on a Markov chain Monte Carlo method to fit our multi-zone two-infall chemical evolution model to the APOGEE DR16 data.

Results. An inside-out formation of the Galaxy disc naturally emerges from the best fit of our two-infall chemical-evolution model to APOGEE-DR16: Inner Galactic regions are assembled on shorter timescales compared to the external ones. In the outer disc (with radii R > 6 kpc), the chemical dilution due to a late accretion event of gas with a primordial chemical composition is the main driver of the [Mg/Fe] versus [Fe/H] abundance pattern in the low-α sequence. In the inner disc, in the framework of the two-infall model, we confirm the presence of an enriched gas infall in the low-α phase as suggested by chemo-dynamical models. Our Bayesian analysis of the recent APOGEE DR16 data suggests a significant delay time, ranging from ∼3.0 to 4.7 Gyr, between the first and second gas infall events for all the analysed Galactocentric regions. The best fit model reproduces several observational constraints such as: (i) the present-day stellar and gas surface density profiles; (ii) the present-day abundance gradients; (iii) the star formation rate profile; and (iv) the solar abundance values.

Conclusions. Our results propose a clear interpretation of the [Mg/Fe] versus [Fe/H] relations along the Galactic discs. The signatures of a delayed gas-rich merger which gives rise to a hiatus in the star formation history of the Galaxy are impressed in the [Mg/Fe] versus [Fe/H] relation, determining how the low-α stars are distributed in the abundance space at different Galactocentric distances, which is in agreement with the finding of recent chemo-dynamical simulations.

Citation

Spitoni, E., Verma, K., Silva Aguirre, V., Vincenzo, F., Matteucci, F., Vaičekauskaitė, B., Palla, M., Grisoni, V., & Calura, F. (2021). APOGEE DR16: A multi-zone chemical evolution model for the Galactic disc based on MCMC methods. Astronomy and Astrophysics, 647, Article A73. https://doi.org/10.1051/0004-6361/202039864

• Journal Article Type: Article
• Acceptance Date: Jan 21, 2021
• Online Publication Date: Mar 10, 2021
• Publication Date: 2021-03
• Deposit Date: Mar 12, 2022
• Publicly Available Date: Mar 31, 2022
• Journal: Astronomy & Astrophysics
• Print ISSN: 0004-6361
• Publisher: EDP Sciences
• Peer Reviewed: Peer Reviewed
• Volume: 647
• Article Number: A73
• DOI: https://doi.org/10.1051/0004-6361/202039864
• Keywords: Space and Planetary Science; Astronomy and Astrophysics
• Public URL: https://hull-repository.worktribe.com/output/3948097