The time-delay model and its applications to galactic archaeology

Abstract

The time-delay model is the way we interpret the diagram [X/Fe] vs. [Fe/H], where X is the abundance of a generic element from carbon to uranium. This interpretation is based on the lifetimes of stars of different masses producing different elements. The abundance of Fe ([Fe/H]) traces the "stellar metallicity" and is due to supernovae Type Ia, which are believed to be the major producers of Fe, and in part to supernovae core-collapse. In particular, if X is an alpha-element, produced on short timescales from massive stars, the ratio [alpha/Fe] will show an overabundance of the alpha-elements relative to Fe at low metallicity. In fact, the bulk of Fe is produced with a time delay relative to alpha-elements, since Type Ia supernovae are white dwarfs in binary systems and they can have lifetimes as long as the age of the Universe. In this paper, I will show how powerful is the time-delay model in order to interpret the abundance patterns observed in stars and interstellar gas, since it allows us to put constraints on stellar nucleosynthesis as well as on the star formation histories of galaxies. I will present some applications of the time-delay model, in particular to the chemical evolution of the Milky Way and galaxies of different morphological type as well as to the identification of high redshift objects by means of their abundances.

Figures (8)

• Figure 1: The [O/Fe] vs. [Fe/H] diagram for the solar vicinity. The models and data are from matteucci1986. The models are described in the text.
• Figure 2: The [X/Fe] vs. [Fe/H] plot for several chemical species, from carbon to zinc in the solar neighborhood. The model predictions are indicated by solid and dashed lines. They differ only for the adopted stellar yields (see romano2010).
• Figure 3: The [Eu/Fe] vs. [Fe/H] plot in the solar neighborhood. The solid curve represents models where Eu is co-produced by CC-SNe and merging neutron stars, while the dashed lines are models with only merging neutron stars. Blue and purple lines refer to different assumptions about the DTD function of merging neutron stars. Note that the DTD$\propto t^{-2}$ (probably unrealistic) predicts many systems merging at early times and therefore it fits much better the data. Black points with error bars are the average observed [Eu/Fe] in a 0.5 dex wide bin. Figure from simonetti2019.
• Figure 4: The [$\alpha$/Fe] vs. [Fe/H] plot in the solar neighborhood. The high-$\alpha$ stars are indicated in red, the low $\alpha$ ones in blue and the intermediate ones in green, The pink line indicates the stars formed during the star formation gap in between the two disks (1%).Figure from spitoni2024.
• Figure 5: The [$\alpha$/Fe] vs. [Fe/H] for three different galactic environments: the Galacticc bulge, the solar vicinity and a Magellanic irregular galaxy. For $\alpha$ we intend a generic $\alpha$-element such as Mg or O. The data reported in the Figure are for the Galactic bulge, LMC and DLAs, as indicated in the figure.