We present photometric properties and distance measurements of 252 high
redshift Type Ia supernovae (0.15 < z < 1.1) discovered during the
first three years of the Supernova Legacy Survey (SNLS). These events
were detected and their multi-colour light curves measured using the
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 performed at the VLT, Gemini and Keck
telescopes to confirm the nature of the supernovae and to measure their
redshifts. Systematic uncertainties arising from light curve modeling
are studied, making use of two techniques to derive the peak magnitude,
shape and colour of the supernovae, and taking advantage of a precise
calibration of the SNLS fields. A flat LambdaCDM cosmological fit to 231
SNLS high redshift Type Ia supernovae alone gives Omega_M = 0.211 +/-
0.034(stat) +/- 0.069(sys). The dominant systematic uncertainty comes
from uncertainties in the photometric calibration. Systematic
uncertainties from light curve fitters come next with a total
contribution of +/- 0.026 on Omega_M. No clear evidence is found for a
possible evolution of the slope (beta) of the colour-luminosity relation
with redshift.
