Subluminous Type Ia Supernovae at High Redshift From the Supernova Legacy Survey

19 pages, 27 figuresThe rate evolution of subluminous Type Ia supernovae (SNe Ia) is presented using data from the Supernova Legacy Survey. This sub-sample represents the faint and rapidly declining light curves of the observed SN Ia population here defined by low-stretch values (s <= 0.8). Up to redshift z = 0.6, we find 18 photometrically identified subluminous SNe Ia, of which six have spectroscopic redshift (and three are spectroscopically confirmed SNe Ia). The evolution of the subluminous volumetric rate is constant or slightly decreasing with redshift, in contrast to the increasing SN Ia rate found for the normal stretch population, although a rising behavior is not conclusively ruled out. The subluminous sample is mainly found in early-type galaxies with little or no star formation, so that the rate evolution is consistent with a galactic mass-dependent behavior: r(z) = A × Mg , with A = (1.1 ± 0.3) × 10-14 SNe yr-1 M -1 sun. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products at the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNR