It's a matter of time: Empirical Constraints on Supernova Yields and Delay Times from Dwarf Spheroidal Galaxies

Abstract

The chemical abundances of a stellar population encode information about nucleosynthesis and its astrophysical sites, but this information is confounded by the specific star formation history of the host galaxy. As a result, placing empirical constraints on supernova yields and timing using abundances has been very challenging. We introduce a galactic chemical evolution model DLEIY that uses an observed star formation history and metallicity distribution to reduce these confounding factors. Using a joint statistical model of the dwarf spheroidal galaxies Sculptor and Fornax, simultaneous constraints on population-averaged yields and galactic outflows are achieved with DLEIY, without fixing the absolute scale of nucleosynthetic yields. The Fe yield from core collapse supernovae is consistent with existing theoretical yield models, while the measured Mg yield is a factor of 2-4 higher, corroborating previous suggestions that yield models may under-predict [Mg/Fe]. We also find that the rate of Type Ia supernovae is enhanced by about a factor of 5 relative to field galaxies, and the delay-time distribution goes as $\sim t^{-2}$, a much steeper relationship than that measured from supernova surveys ($\sim t^{-1.1}$). These findings may suggest a metallicity dependence of the Type Ia rate and delay-time distribution.

Figures (13)

• Figure 1: Schematic representation of DLEIY. (Left) The observed SFH and MDF are used to construct an age-metallicity relation. (Center) The age-metallicity relation, a parameterization of SN-driven outflows, and nucleosynthesis prescriptions (a delay-time distribution and population-averaged yields for different sources) are used to model the chemical abundances and gas mass (Right).
• Figure 2: Graphical representation of the independent, shared-yield, and shared-yield+DTD models. The independent model has $7n$ parameters, where $n$ is the number of galaxies, as all parameters are unique to each galaxy. The shared-yield model has $4n+3$ parameters, and the shared-yield+DTD model has $2n+5$ parameters.
• Figure 3: The downstream effects of using the observed MDF (blue) versus the deconvolved MDF (green) in DLEIY. The observed MDF (top row) leads to more significant bias in the AZR (middle row), which induces bias in the predicted chemical abundance track (bottom row).
• Figure 4: Median residuals (with 16/84% credible interval) for a grid of tests using mock galaxies made with VICE johnson_dwarf_2023. We use the shared-yield model on Sculptor- and Fornax-like mock galaxies for varying sample sizes and uncertainties.
• Figure 5: Posterior distributions for the DTD slope parameter $\alpha$ for two mock Sculptor-like galaxies with different DTDs, with the median and 0.3/99.7% credible interval demarcated by vertical lines. The region of overlap is highlighted. The distributions can be distinguished at $\sim2.5\sigma$. This mock test was run using the shared-yield model.