Using chemical evolution models of the Milky Way disk to constrain Type Ia supernova progenitors

Context. Thermonuclear explosions of carbon-oxygen white dwarfs as Type Ia supernovae (SNe Ia) play a significant role in the galactic chemical evolution (GCE) of the Milky Way. However, a long-standing and as yet unresolved problem of modern astrophysics concerns the identity of their progenitor. Aims. We aim to use GCE predictions to help constrain potential SN Ia progenitor scenarios, since it is well known that SN Ia nucleosynthesis yields, in particular the Fe-peak elements, depend on the explosion mechanism. Methods. We calculated 1140 GCE models and compared the GCE-predicted abundance ratios for four different SN Ia explosion mechanisms – two from sub-Chandrasekhar ( M Ch ) mass progenitors and two from near- M Ch mass progenitors – to spectroscopic measurements of Milky Way disk stars, considering both local thermodynamic equilibrium (LTE) and non-LTE (NLTE) assumptions. We calibrated the GCE framework for two sets of massive star yields in order to assess how stellar modelling uncertainties affect the relative contribution from core-collapse supernovae (CCSNe) towards Si, Ca, and the Fe-peak elements. Results. From a GCE perspective, Si and Ca cannot be used to constrain SN Ia progenitors since there is little variation in their yields between different explosion types. The GCE of [Ti/Fe] and [Co/Fe] are not reproduced by any combination of yields. The [Cr/Fe] ratio is also problematic, since hardly any NLTE data of the disk are available and there are conflicting yields from CCSNe. For [Mn/Fe], neither CCSN yield set are compatible with the NLTE data. For [Ni/Fe], the NLTE data are well fit by one set of CCSN yields, with the best-fitting GCE models having a ∼85% contribution from sub- M Ch SNe Ia. Conclusions. We advise caution when using GCE models to constrain the Galaxy’s SN Ia population, since the results depend on both the choice of CCSN yields and the elemental ratio used as a diagnostic.