Supernova Archaeology: Uncovering the origins of thermonuclear supernovae from clues in the ISM

Type Ia supernovae (SNe Ia) have proven vital to our understanding of cosmology, both as standard candles and for their role in the origin of the elements. They are now understood to arise from the thermonuclear explosion of a white dwarf, but why should a white dwarf explode? Evolutionary models can be grouped into either "accretion" or "merger" scenarios, with accretion models typically implying a hot, luminous phase prior to explosion. These objects are significant sources of ionizing radiation; therefore, the environment surrounding SN Ia progenitors should be strongly ionized, and traced by faint nebular emission. Such "relic" nebulae should extend out to 10 -- 100 parsecs and linger for roughly the recombination timescale in the ISM (∼100,000 years). In this talk, I'll show how the absence of a surrounding nebula excludes any accretion ("single-degenerate") channel for the origin of Tycho's supernova, as well as many other nearby remnants. Most variations on the merger ("double degenerate") scenario remain viable. I'll also show how a similar test can be applied to the integrated emission of old stellar populations, ruling out the textbook accretion scenario for delay times greater than 1 Gyr, before concluding with some recent results on the deeper connections between binary progenitors of some supernovae and the diffuse ionized gas of spiral galaxies.