Manganese Indicates a Transition from Sub- to Near-Chandrasekhar Type Ia Supernovae in Dwarf Galaxies

Abstract

Manganese abundances are sensitive probes of the progenitors of Type Ia supernovae (SNe Ia). In this work, we present a catalog of manganese abundances in dwarf spheroidal satellites of the Milky Way, measured using medium-resolution spectroscopy. Using a simple chemical evolution model, we infer the manganese yield of SNe Ia in the Sculptor dwarf spheroidal galaxy (dSph) and compare to theoretical yields. The sub-solar yield from SNe Ia ([(Mn/Fe)_(Ia) = -0.30_(-0.03)^(+0.03) at [Fe/ H] = −1.5 dex, with negligible dependence on metallicity) implies that sub-Chandrasekhar-mass (sub-M_(Ch)) white dwarf progenitors are the dominant channel of SNe Ia at early times in this galaxy, although some fraction (≳ 20%) of M_(Ch) Type Ia or Type Iax SNe are still needed to produce the observed yield. First-order corrections for deviations from local thermodynamic equilibrium increase the inferred [(Mn/Fe)]_Ia by as much as ~0.3 dex. However, our results also suggest that the nucleosynthetic source of SNe Ia may depend on environment. In particular, we find that dSphs with extended star formation histories (Leo I, Fornax dSphs) appear to have higher [Mn/Fe] at a given metallicity than galaxies with early bursts of star formation (Sculptor dSph), suggesting that M Ch progenitors may become the dominant channel of SNe Ia at later times in a galaxy's chemical evolution.