Modelling the chemical evolution of Zr, La, Ce, and Eu in the Galactic discs and bulge

Abstract

We study the chemical evolution of Zr, La, Ce and Eu in the Milky Way discs and bulge by means of chemical evolution models compared with spectroscopic data. We consider detailed chemical evolution models for the Galactic thick disc, thin disc and bulge, which have been already tested to reproduce the observed [α/Fe] vs. [Fe/H] diagrams and metallicity distribution functions for the three different components, and we apply them to follow the evolution of neutron capture elements. In the [Eu/Fe] vs. [Fe/H] diagram, we observe and predict three distinct sequences corresponding to the thick disc, thin disc and bulge, similarly to what happens for the α-elements. We can nicely reproduce the three sequences by assuming different timescales of formation and star formation efficiencies for the three different components, with the thin disc forming on a longer timescale of formation with respect to the thick disc and bulge. On the other hand, in the [X/Fe] vs. [Fe/H] diagrams for Zr, La and Ce, the three populations are mixed and also from the model point of view there is an overlapping between the predictions for the different Galactic components, but the observed behaviour can be also reproduced by assuming different star formation histories in the three components. In conclusions, it is straightforward to see how different star formation histories can lead to different abundance patterns and also looking at the abundance patterns of neutron capture elements can help in constraining the history of formation and evolution of the major Galactic components.

Nitrogen evolution in the halo, thick disc, thin disc and bulge of the Galaxy

“…• Then, in order to focus on the Galactic thick and thin discs and to study separately these two components, we take advantage of the parallel model of Grisoni et al (2017), where we implement the reference nucleosynthesis prescriptions as previously established. We conclude that the thick disc had a much faster evolution with respect to the thin disc, in accordance with results for other chemical elements, like the α-elements (Grisoni et al 2017, lithium (Grisoni et al 2019, 2020a, Romano et al 2021, carbon (Romano et al 2020), fluorine (Grisoni et al 2020b) and neutron-capture elements (Grisoni et al 2020c).…”

“…Then, to focus on the thick and thin discs, we make use of the parallel model of Grisoni et al (2017) (see also Chiappini 2009), that enables to study separately the evolution in the discs. This chemical evolution model has already been constrained to fit the [α/Fe] vs. [Fe/H] plots and the metallicity distribution functions (MDFs) in the thick and thin discs (Grisoni et al 2017(Grisoni et al , 2018, and also the abundance diagrams of various elements like lithium , 2020a, Romano et al 2021, carbon (Romano et al 2020), fluorine (Grisoni et al 2020b), r-and s-process elements (Grisoni et al 2020c), and here we adopt it to focus on the evolution of N in the thick disc and thin disc. Moreover, we will apply the model of Matteucci et al (2019Matteucci et al ( , 2020 for the Galactic bulge to follow nitrogen evolution also in this Galactic component.…”

On the effects of the Initial Mass Function on Galactic chemical enrichment

“…None of the chemical evolution models calibrated on the thin disc is able to reproduce the [O/Fe] trend of the thick disc. To reproduce the higher values of the α-enhancement seen in thick disc stars one need to change the chemical evolution parameters in particular reduce the infall timescale to τ in f =0.5 Gyr and increase the star formation efficiency to ν=1.4 Gyr −1 , in agreement with the literature (Grisoni et al 2019(Grisoni et al , 2020a. The MDF of thick disc stars is well reproduced with these parameters but, in order to better fit its fast decreasing tail at the higher metallicity with our simple chemical evolution model, we need to im-pose a galactic wind at an age of 2.5 Gyr.…”

On the variation of carbon abundance in galaxies and its implications

“…2. The parallel model proposed by Grisoni et al (2017) that envisages distinct formation sequences for the thick and thin discs (see also Grisoni et al 2019Grisoni et al , 2020. In the parallel model, the two discs form independently on different timescales out of two separate infall episodes.…”

“…The chemical evolution models adopted in this study track the evolution of the chemical composition of the interstellar medium (ISM) in different galaxies and/or Galactic components. They deal with several elements, from the lightest ones emerging from Big Bang nucleosynthesis (Romano et al 2003) to the heaviest ones synthesised by uncommon astrophysical sites, like magneto-rotational driven SNe, and/or through rare events, as compact binary mergers (Matteucci et al 2014;Cescutti et al 2015;Grisoni et al 2020).…”