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Supernova Rates, Rise-Times, and their Relations to Progenitors

Santiago Gonzalez Gaitan

Doctor of Philosophy 2011
Graduate Department of Astronomy and Astrophysics, University of Toronto

Supernovae are fundamental in astronomy: they inject high mass elements into the interstellar medium enriching the chemistry of galaxies, they feed processes of star formation and active galactic nuclei, and they have been a key for the developments in cosmology of the past decades.

This dissertation presents a set of subluminous type Ia supernovae (SNe Ia) at z > 0.1 from the Supernova Legacy Survey (SNLS). These faint and short-lived transients are found in massive and passive host galaxies. We measure a volumetric rate as a function of redshift that is different from the normal SN Ia population. The observations point towards a long delay time since the birth of the progenitors systems and argue for progenitor stars of initial low mass.

We calculate a stretch-corrected rise-time since explosion to maximum brightness for different sets of SNe Ia. We find that a fiducial 17 day quadratic rise is sufficient to explain all SNe Ia, including subluminous ones, arguing for their homogeneity throughout the entire light-curve. Subluminous SNe Ia are powered by as little as 0.05 Msolar of 56Ni synthesized in the explosion. Theoretical models need to explain these challenging weak explosions within the framework of SNe Ia.

Finally, we develop one of the first robust automated techniques to identify plateau supernovae (SNe IIP) in large photometric transient surveys. This simple method was tested with a variety of real and simulated SN samples and proved to be effective across different redshifts. Such a photometric typing will be of great power for coming surveys and will allow numerous scientific studies of SNe IIP.

Reproduced with permission. library@astro.utoronto.ca
October 4, 2011