SPITONI, EmanueleEmanueleSPITONIVerma, K.K.VermaSilva Aguirre, V.V.Silva AguirreMATTEUCCI, Maria FrancescaMaria FrancescaMATTEUCCIVaičekauskaitė, B.B.VaičekauskaitėPALLA, MARCOMARCOPALLAGRISONI, ValeriaValeriaGRISONICALURA, FrancescoFrancescoCALURAVincenzo, FiorenzoFiorenzoVincenzo2025-02-202025-02-2020210004-6361http://hdl.handle.net/20.500.12386/36100Context. 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]. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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.STAMPAenArticle10.1051/0004-6361/2020398642-s2.0-85102336116http://arxiv.org/abs/2101.08803v1https://www.aanda.org/articles/aa/full_html/2021/03/aa39864-20/aa39864-20.html2021A&A...647A..73SFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation