The ESO/VLT 3rd year Type Ia supernova data set from?the?supernova?legacy?survey

摘要

Aims. We present 139 spectra of 124 Type Iasupernovae (SNeIa) that were observed at the ESO/VLT duringthe first three years of the Canada-France-Hawa? Telescope (CFHT)supernova legacy survey (SNLS). This homogeneous data set is used totest for redshift evolution of SNIa spectra, and will be usedin the SNLS 3rd year cosmological analyses. Methods. Spectra have been reduced and extractedwith a dedicated pipeline that uses photometric information from deepCFHT legacy survey (CFHT-LS) reference images to trace, at sub-pixelaccuracy, the position of the supernova on the spectrogram as afunction of wavelength. It also separates the supernova and its hostlight in 60%of cases. The identification of the supernova candidates is performedusing a spectrophotometric SNIa model. Results. A total of 124 SNeIa, roughly 50%of the overall SNLS spectroscopic sample, have been identified usingthe ESO/VLT during the first three years of the survey. Their redshiftsrange from z=0.149 to z=1.031.The average redshift of the sample is.This constitutes the largest SNIa spectral set to date inthis redshift range. The spectra are presented along with theirbest-fit spectral SNIa model and a host model where relevant.In the latter case, a host subtracted spectrum is also presented. Weproduce average spectra for pre-maximum, maximum and post-maximumepochs for both z<0.5 and SNeIa. We find that z<0.5 spectrahave deeper intermediate mass element absorptions than spectra. The differences with redshift are consistent with theselection of brighter and bluer supernovae at higher redshift. Key words: cosmology: observations -supernovae: general - methods: data analysis - techniques:spectroscopic