Evidence for Sub-Chandrasekhar Type Ia Supernovae from Stellar Abundances in Dwarf Galaxies

There is no consensus on the progenitors of Type. Ia supernovae (SNe Ia) despite their importance for cosmology and chemical evolution. We address this question using our previously published catalogs of Mg, Si, Ca, Cr, Fe, Co, and Ni abundances in dwarf galaxy satellites of the Milky Way (MW) to constrain the mass at which the white dwarf (WD) explodes during a typical SN. Ia. We fit a simple bi-linear model to the evolution of [X/Fe] with [Fe/H], where X represents each of the elements mentioned above. We use the evolution of [Mg/Fe] coupled with theoretical supernova yields to isolate what fraction of the elements originated in SNe. Ia. Then, we infer the [X/Fe] yield of SNe. Ia for all of the elements except Mg. We compare these observationally inferred yields to recent theoretical predictions for two classes of Chandrasekhar-mass (M-Ch) SN. Ia as well as sub-M-Ch SNe. Ia. Most of the inferred SN. Ia yields are consistent with all of the theoretical models, but [Ni/Fe] is consistent only with sub-M-Ch models. We conclude that the dominant type of SN. Ia in ancient dwarf galaxies is the explosion of a sub-M-Ch WD. The MW and dwarf galaxies with extended star formation histories have higher [Ni/Fe] abundances, which could indicate that the dominant class of SN. Ia is different for galaxies where star formation lasted for at least several Gyr.