Galactic Archaeology with chemical evolution models
Emanuele Spitoni (Aarhus University)
Tuesday 02/07/2019 @ 14:00, Sala IV piano Battiferro
Precise stellar ages from asteroseismology have become available and can help setting stronger constraints on the evolution of the Galactic disc components. Recently, asteroseismology has confirmed a clear age difference in the solar annulus between two distinct sequences in the [alpha/Fe] versus [Fe/H] abundance ratios relation: the high-alpha and low-alpha stellar populations. We show that in the classical `two-infall' model (the high-alpha phase forms by a fast gas accretion episode and the low-alpha sequence follows later from a slower gas infall rate), a consistent delay of ~4.3 Gyr in the beginning of the second gas accretion episode is a crucial assumption to reproduce stellar abundances and ages. The revised `two-infall' model including uncertainties in age and metallicity is capable of reproducing: i) the [alpha/Fe] vs. [Fe/H] abundance relation at different Galactic epochs, ii) the age-metallicity relation and the time evolution [alpha/Fe]; iii) the age distribution of the high-alpha and low-alpha stellar populations, iv) the metallicity distribution function. Moreover, we discuss the hypothesis that the consistent delay is originated by merger events between the Galaxy and systems like Enceladus. In the last part of my talk I will show recent results related to azimuthal variation of abundance gradients in the Milky Way. We quantify the effects of spiral arm density fluctuations on the azimuthal variations of the oxygen abundances in the Galactic disk. We interpret the presence of azimuthal scatter at all radii by the presence of multiple spiral modes moving at different pattern speeds.