Manganese spread in Ursa Minor as a proof of sub-classes of type Ia supernovae

TL;DR

This study investigates how new subclasses of Type Ia supernovae, with distinct nucleosynthesis yields, influence chemical evolution in dwarf galaxies, providing evidence for their existence through manganese abundance patterns.

Contribution

The paper introduces a stochastic chemical evolution model that incorporates new SNe Ia subclasses, explaining observed manganese and alpha-element trends in Ursa Minor.

Findings

Predicted a butterfly-shaped [Mn/Fe] spread at low metallicity.

Found a decrease in [alpha/Fe] ratios at lower [Fe/H] than in the solar neighborhood.

Model results align with observed stellar abundances in Ursa Minor.

Abstract

Context. Recently, new sub-classes of Type Ia supernovae (SNe Ia) were discovered, including SNe Iax. The suggested progenitors of SNe Iax are relatively massive, possibly hybrid C+O+Ne white dwarfs, which can cause white dwarf winds at low metallicities. There is another class that can potentially occur at low or zero metallicities; sub-Chandrasekhar mass explosions in single and/or double degenerate systems of standard C+O white dwarfs. These explosions have different nucleosynthesis yields compared to the normal, Chandrasekhar mass explosions. Aims. We test these SN Ia channels using their characteristic chemical signatures. Methods. The two sub-classes of SNe Ia are expected to be rarer than normal SNe Ia and do not affect the chemical evolution in the solar neighbourhood; however, because of the shorter delay time and/or weaker metallicity dependence, they could influence the evolution of metalpoor systems. Therefore, we have included both in our stochastic chemical evolution model for the dwarf spheroidal galaxy Ursa Minor. Results. The model predicts a butterfly-shape spread in [Mn/Fe] in the interstellar medium at low metallicity and - at the same time - a decrease of [alpha/Fe] ratios at lower [Fe/H] than in the solar neighbourhood, both of which are consistent with the observed abundances in stars of Ursa Minor. Conclusions. The surprising agreement between our models and available observations provides a strong indication of the origins of these new sub-classes of SNe Ia. This outcome requires confirmation by future abundance measurements of manganese in stars of other satellite galaxies of ourMilkyWay. It will be vital for this project to measure not the most extreme metal-poor tail, as more commonly happens, but the opposite; the metal-rich end of dwarf spheroidals.