SNLS: The Supernova Type Ia Rate at z = 0.47

• Main Authors: Neill, J. D., Sullivan, M., Balam, D., Astier, P., Aubourg, E., Basa, S., Carlberg, R. G., Conley, A., Fabbro, S., Fouchez, D., Guy, J., Hook, I., Howell, D. A., Lafoux, H., Pain, R., Palanque-Delabrouille, N., Perrett, K., Pritchet, C. J., Regnault, N., Rich, J., Taillet, Richard, Baumont, S., Bronder, J., Graham, M., Hsiao, E., Lusset, V., Ripoche, P., Mourao, A., Perlmutter, S., Tao, C.
• Format: Conference Proceeding
• Language: English
• Subjects: Astrophysics; Cosmology and Extra-Galactic Astrophysics; Physics
• ISSN: 0002-7537

We present a preliminary measurement of the distant Type Ia supernova rate derived from the Canada -- France -- Hawaii Telescope Supernova Legacy Survey (SNLS). By observing four one-square degree fields with a high temporal frequency (< $\delta$ > ~4 observer-frame days) over large fractions of a year (~6 months each field, with breaks during full moon) and using 8 meter-class telescopes for spectroscopic followup, the survey not only provides the dense time sampling needed to achieve a high completeness, but also enjoys the benefit of high quality spectroscopy to verify the Type Ia candidates and hence reduce contamination from non-Type Ia events. The goal of the survey is to measure ~ 700 Type Ia SNe out to $z ^~ 1$ over a period of 5 years. We use the first two years of survey data to begin characterizing the Type Ia sample and explore a methodology for calculating rates from the survey. We use individual SNLS survey epoch properties to observe Monte Carlo simulations of $10^6 $Type Ia supernovae in the redshift range 0.2 < z < 0.6, and thus derive our survey efficiency. We combine this efficiency with a carefully selected control sample of spectroscopically confirmed SNLS Type Ia SNe to derive a volumetric rate. When comparing our volumetric rate with other ground-based surveys that also use spectroscopic candidate verification, we find no evidence for significant systematic underestimation of the SN Ia rates near z = 0.5. When comparing published SN Ia rates spanning the redshift range 0.0 < z < 1.6 to models of SN Ia production, we find that neither pure delay-time models nor two component models can accommodate all the observed data.