The Progenitors of Subluminous Type I[CLC]a[/CLC] Supernovae

Abstract

We find that spectroscopically peculiar subluminous Type Ia supernovae (SNe Ia) come from an old population. Of the 16 subluminous SNe Ia known, 10 are found in E/S0 galaxies, and the remainder are found in early-type spiral galaxies. The probability that this is a chance occurrence is only 0.2%. The finding that subluminous SNe Ia are associated with an older stellar population indicates that for a sufficiently large look-back time (already accessible in current high-redshift searches) they will not be found. Due to a scarcity in old populations, hydrogen and helium main-sequence stars and He red giant stars that undergo Roche lobe overflow are unlikely to be the progenitors of subluminous SNe Ia. Earlier findings that overluminous SNe Ia [Δm 15 (B) ≲ 0.95] come from a young progenitor population are confirmed. The fact that subluminous SNe Ia and overluminous SNe Ia come from different progenitor populations and also have different properties is a prediction of the CO white dwarf merger progenitor scenario.