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Louis G. Strolger |
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I will present the state of the current observational constraints on SN Ia progenitors, based on volumetric rate measures (to z = 2) and host galaxy demographics. At present, SNe Ia in high and low redshift galaxies show inconsistent results on the implied progenitors responsible for these important cosmological tools. At its heart, the debate now hinges on two important factors: (1) the metallicity of the progenitor and its impact on event luminosity and production efficiency; and (2) the time required for a SN~Ia progenitor system to develop to an explosion from an episode of star-formation (commonly called the ``delay time''). While these are conceptually measurable factors in low redshift (z < 0.1) galaxies, attempts to do so have been muddled by two degenerate effects: (1) population age, which steadily increases the range of metallicity within a given environment, and (2) rate of active star formation, which mix-up the incubation time between SN events and progenitor formation. Results from high redshift (z > 1) surveys, which by the nature of being age-limited surveys should elucidate the nature of SNe Ia, have instead implied very long (3 to 4 Gyr) delay times that are largely inconsistent with the relatively short (< 1 Gyr) times predicted from binary star evolutionary models and low-z observations. |