On the origin of the Galactic thin and thick discs, their abundance gradients and the diagnostic potential of their abundance ratios

Abstract

Using a semi-analytical model of the evolution of the Milky Way, we show how secular evolution can create distinct overdensities in the phase space of various properties (e.g. age vs metallicity or abundance ratios vs age) corresponding to the thin and thick discs. In particular, we show how key properties of the Solar vicinity can be obtained by secular evolution, with no need for external or special events, like galaxy mergers or paucity in star formation. This concerns the long established double-branch behaviour of [alpha/Fe] vs metallicity and the recently found non-monotonic evolution of the stellar abundance gradient, evaluated at the birth radii of stars. We extend the discussion to other abundance ratios and we suggest a classification scheme, based on the nature of the corresponding yields (primary vs secondary or odd elements) and on the lifetimes of their sources (short-lived vs long-lived ones). The latter property is critical in determining the single- or double- branch behavior of an elementary abundance ratio in the Solar neighborhood. We underline the high diagnostic potential of this finding, which can help to separate clearly elements with sources evolving on different timescales and help determining the site of e.g. the r-process(es). We define the ‘abundance distance’ between the thin and thick disc sequences as an important element for such a separation. We also show how the inside-out evolution of the Milky Way disc leads rather to a single-branch behavior in other disc regions.

A Perspective on the Milky Way Bulge Bar as Seen from the Neutron-capture Elements Cerium and Neodymium with APOGEE

“…Indeed, the efficiency of the s-process in low-mass stars is known to increase with metallicity and go through a maximum at a value that depends on the mass number of the isotope: the production of heavier isotopes reaches that maximum at lower metallicity values than lighter ones (see, e.g., Figure 1 in Travaglio et al 2004). For that reason, the evolution of the [s-/Fe] ratio of elements of the second s-peak, like Ba or Ce, is expected to display a small bump at slightly subsolar metallicities, as found in Figure 5 of Travaglio et al (2004), Figure 2 of Grisoni et al 2020, or in Prantzos et al (2018 for one-zone models (their Figure 16) and Prantzos et al (2023;their Figure 14), which adopt different sets of yields (see the discussion in the first paragraph of Section 5).…”

Presupernova Evolution and Explosive Nucleosynthesis of Rotating Massive Stars. II. The Supersolar Models at [Fe/H] = 0.3

“…Thorsbro et al (2020), Feldmeier-Krause (2022), and Nogueras-Lara et al (2023), for example, by analyzing quite a large number of giants in the Galactic center, have shown that the metallicities of these stars reaches up to 10 times the solar metallicity. Therefore, the use of stellar yields from SSM sources is essential to study the formation and the chemical evolution of these regions (Cinquegrana & Karakas 2022;Prantzos et al 2023). Furthermore, we note that the yields we present in this paper have already been adopted by Prantzos et al (2023).…”

“…Therefore, the use of stellar yields from SSM sources is essential to study the formation and the chemical evolution of these regions (Cinquegrana & Karakas 2022;Prantzos et al 2023). Furthermore, we note that the yields we present in this paper have already been adopted by Prantzos et al (2023).…”

“…A few years ago (hereinafter LC18) published an extended set of models and yields of massive stars in the metallicity range −3 [Fe/H] 0 and with initial rotation velocities in the range 0-300 km s −1 . Those results were mainly intended as a database to be used in galactic chemical evolution (GCE) models (e.g., Prantzos et al 2018;Palla et al 2022;Vasini et al 2022;Pignatari et al 2023;Prantzos et al 2023;Womack et al 2023). In an additional paper (Roberti et al 2024) we explored the influence of rotation on the evolution and nucleosynthesis of massive stars also at metallicities between primordial (Z = 0) and [Fe/H] = −4.…”

“…LC18 were the first to provide an extended set of homogeneous yields coming from the evolution and explosion of massive stars in the range 13-120 M e . Moreover, LC18 and Prantzos et al (2018Prantzos et al ( , 2023 showed that rotation may also increase the production of fluorine and that this is crucial to explain the F evolution in the Galaxy. Despite all the large amount of work done on the influence of rotation on the yields produced by CCSNe, a study of the impact of rotation on the yields of SSM massive-star models is still missing.…”