The Supernova Legacy Survey: Measurement ofM, and w from the First Year Data Set ⋆

We present distance measurements to 71 high redshift type Ia supernovae discovered during the first year of the 5-year Supernova Legacy Survey (SNLS). These events were detected and their multi-color light-curves measured using t he MegaPrime/MegaCam instrument at the Canada-France-Hawaii Telescope (CFHT), by repeatedly imaging four one-square degree fields in four bands. Follow-up spectroscopy was perf ormed at the VLT, Gemini and Keck telescopes to confirm the nature of the supernovae and to measure their redshift. With this data set, we have built a Hubble diagram extending to z = 1, with all distance measurements involving at least two bands. Systematic uncertainties are evaluated making use of the multi- band photometry obtained at CFHT. Cosmological fits to this fi rst year SNLS Hubble diagram give the following results : M = 0.263± 0.042 (stat)± 0.032 (sys) for a flatCDM model; and w = −1.023± 0.090 (stat)± 0.054 (sys) for a flat cosmology with constant equation of state w when combined with the constraint from the recent Sloan Digital Sky Survey measurement of baryon acoustic oscillations.