The Relationship between Age, Metallicity, and Abundances for Disk Stars in a Simulated Milky Way

Abstract

Observations of the Milky Way’s low-α disk show that several element abundances correlate with age at fixed metallicity, with unique slopes and small scatters around the age–[X/Fe] relations. In this study, we turn to simulations to explore the age–[X/Fe] relations for the elements C, N, O, Mg, Si, S, and Ca that are traced in a FIRE-2 cosmological zoom-in simulation of a Milky Way–like galaxy, m12i, and understand what physical conditions give rise to the observed age–[X/Fe] trends. We first explore the distributions of mono-age populations in their birth and current locations, [Fe/H], and [X/Fe], and find evidence for inside-out radial growth for stars with ages <7 Gyr. We then examine the age–[X/Fe] relations across m12i’s disk and find that the direction of the trends agrees with observations, apart from C, O, and Ca, with remarkably small intrinsic scatters, σ int (0.01 − 0.04 dex). This σ int measured in the simulations is also metallicity dependent, with σ int ≈ 0.025 dex at [Fe/H] = −0.25 dex versus σ int ≈ 0.015 dex at [Fe/H] = 0 dex, and a similar metallicity dependence is seen in the GALAH survey for the elements in common. Additionally, we find that σ int is higher in the inner galaxy, where stars are older and formed in less chemically homogeneous environments. The age–[X/Fe] relations and the small scatter around them indicate that simulations capture similar chemical enrichment variance as observed in the Milky Way, arising from stars sharing similar element abundances at a given birth place and time.

Unveiling the time evolution of chemical abundances across the Milky Way disc with APOGEE

“…Our method also reproduces R birth distributions found in state-of-the-art simulations (e.g. Agertz et al 2021 ;Carrillo et al 2023 ). In contrast to Minchev et al ( 2018 ), who imposed such shifting in the peaks of mono-R birth populations in order to estimate the Milky Way's ∇[Fe / H]( τ ), here we reach a very similar configuration directly from the data, as described abo v e.…”

“…If R birth can be reco v ered using the observed age and [Fe / H] ( Minchev et al 2018 ;Lu et al 2022a ), as it also appears to be the case in cosmological simulations of Milky Way-like galaxy discs (Feltzing, Bowers & Agertz 2020 ), then this should have implications for all other chemical elements. Indeed, Ness et al ( 2019 ), Sharma et al ( 2022 ), andCarrillo et al ( 2023 ) (using APOGEE, GALAH , and cosmological zoom-in simulations, respectively) demonstrated that for stars in small bins of [Fe / H] and age, all other abundances had very small scatter. More recently, Hayden et al ( 2022 ) used the correlation between age, [Fe / H], and elemental abundances to estimate ages for the GALAH dataset, thus using properties of stars born at the same time and place without actually reco v ering R birth (see also He, Luo & Chen 2022 ).…”

Analyzing the cosmic architecture in the vicinity of Grand-design and Flocculent spiral galaxies with Local Geometric Index

“…• The age-metallicity relationship is reportedly uncorrelated or anti-correlated, according to a number of studies [90][91][92][93]. However, the mass and star-formation histories of the galaxies as well as their environments affect the age-metallicity slope.…”

Living with a Red Dwarf: X-Ray, UV, and Ca ii Activity–Age Relationships of M Dwarfs

“…In effect, the X-ray relationship extends the range over which more reliable ages can be determined for early M dwarfs. Additional methods of age determination involving kinematics (Lu et al 2021) and abundances (Carrillo et al 2023) can also be employed to achieve results based on as many techniques as the data allow. This opportunity to determine M dwarf ages through multiple methods, or to compare the ages of each method for targets with high-quality data, holds great potential for future studies.…”