Supernova Legacy Survey: Using Spectral Signatures To Improve Type Ia
  Supernovae As Distance Indicators
  GMOS optical long-slit spectroscopy at the Gemini-North telescope was used to
classify targets from the Supernova Legacy Survey (SNLS) from July 2005 and May
2006 - May 2008. During this time, 95 objects were observed. Where possible the
objects' redshifts (z) were measured from narrow emission or absorption
features in the host galaxy spectrum, otherwise they were measured from the
broader supernova features. We present spectra of 68 confirmed or probable SNe
Ia from SNLS with redshifts in the range 0.17 \leq z \leq 1.02. In combination
with earlier SNLS Gemini and VLT spectra, we used these new observations to
measure pseudo-equivalent widths (EWs) of three spectral features - CaII H&K,
SiII and MgII - in 144 objects and compared them to the EWs of low-redshift SNe
Ia from a sample drawn from the literature. No signs of changes with z are seen
for the CaII H&K and MgII features. Systematically lower EW SiII is seen at
high redshift, but this can be explained by a change in demographics of the SNe
Ia population within a two-component model combined with an observed
correlation between EW SiII and photometric lightcurve stretch.
