Abstract
Abstract We demonstrate that using up to seven stellar abundance ratios can place observational constraints on the star formation histories (SFHs) of Local Group dSphs, using Sculptor dSph as a test case. We use a one-zone chemical evolution model to fit the overall abundance patterns of α elements (which probe the core-collapse supernovae that occur shortly after star formation), s-process elements (which probe AGB nucleosynthesis at intermediate delay times), and iron-peak elements (which probe delayed Type Ia supernovae). Our best-fit model indicates that Sculptor dSph has an ancient SFH, consistent with previous estimates from deep photometry. However, we derive a total star formation duration of ∼0.9 Gyr, which is shorter than photometrically derived SFHs. We explore the effect of various model assumptions on our measurement and find that modifications to these assumptions still produce relatively short SFHs of duration ≲1.4 Gyr. Our model is also able to compare sets of predicted nucleosynthetic yields for supernovae and AGB stars, and can provide insight into the nucleosynthesis of individual elements in Sculptor dSph. We find that observed [Mn/Fe] and [Ni/Fe] trends are most consistent with sub-M Ch Type Ia supernova models, and that a combination of “prompt” (delay times similar to core-collapse supernovae) and “delayed” (minimum delay times ≳50 Myr) r-process events may be required to reproduce observed [Ba/Mg] and [Eu/Mg] trends.
Highlights
Inside a star-forming galaxy, baryonic matter is constantly cycling between two phases of matter: stars and the interstellar medium (ISM)
Like previous one-zone Galactic chemical evolution (GCE) models, our model fits the trends of the α elements Mg, Si, and Ca, which probe core-collapse supernovae (CCSNe), and Fe, which is predominantly produced by Type Ia supernovae
Our model is able to fit the observed abundances of C and Ba, which trace nucleosynthesis in asymptotic giant branch (AGB) stars
Summary
Inside a star-forming galaxy, baryonic matter is constantly cycling between two phases of matter: stars and the interstellar medium (ISM). The ISM, which is predominantly gas, contains the raw material that forms stars; stars produce heavy elements throughout their lifetimes, release them back into the ISM when they die This cycle is not closed—stars can produce outflows that remove gas from a galaxy (Mathews & Baker 1971; Larson 1974), and inflows of gas can add metal-poor material to a galaxy (Larson 1972; Dekel et al 2009). The SEDs may be composed of broadband photometry (e.g., Smith & Hayward 2015) or a continuous spectrum of the integrated light of the galaxy’s stars and ionized gas (e.g., Magris C. et al 2015) This method is useful for obtaining SFHs of distant, unresolved galaxies, it depends strongly on prior assumptions about the model SFHs (Carnall et al 2019; Leja et al 2019), as well as the stellar initial mass function (IMF) (Conroy & Van Dokkum 2012, among others)
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