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

¹ LPNHE, CNRS-IN2P3 and Universities of Paris 6 & 7, 75252 Paris Cedex 05, France e-mail: balland@lpnhe.in2p3.fr
² University Paris 11, 91405 Orsay, France
³ LAM, CNRS, BP8, Pôle de l'étoile, Site de Château-Gombert, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁴ APC, UMR 7164 CNRS, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France
⁵ LUTH, UMR 8102 CNRS, Observatoire de Paris, Section de Meudon, 92195 Meudon Cedex, France
⁶ Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102, Goleta, CA 93117, USA
⁷ Department of Physics, University of California, Santa Barbara, Broida Hall, Mail Code 9530, Santa Barbara, CA 93106-9530, USA
⁸ Department of Astronomy and Astrophysics, 50 St. George Street, Toronto, ON M5S 3H4, Canada
⁹ CPPM, CNRS-Luminy, Case 907, 13288 Marseille Cedex 9, France
¹⁰ University of Oxford, Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
¹¹ Department of Physics and Astronomy, University of Victoria, PO Box 3055, Victoria, BC V8W 3P6, Canada
¹² CEA/Saclay, DSM/Irfu/Spp, 91191 Gif-sur-Yvette Cedex, France
¹³ CENTRA-Centro M. de Astrofisica and Department of Physics, IST, Lisbon, Portugal
¹⁴ SIM/IDL, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, C8, 1749-016 Lisbon, Portugal
¹⁵ Oskar Klein Center, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
¹⁶ CRAL, Observatoire de Lyon; CNRS, UMR 5574; ENS de Lyon, France
¹⁷ Université de Lyon, 69622, Lyon, France; Université Lyon 1, France

Received: 1 April 2009
Accepted: 20 August 2009

Abstract

Aims. We present 139 spectra of 124 Type Ia supernovae (SNe Ia) that were observed at the ESO/VLT during the first three years of the Canada-France-Hawaï Telescope (CFHT) supernova legacy survey (SNLS). This homogeneous data set is used to test for redshift evolution of SN Ia spectra, and will be used in the SNLS 3rd year cosmological analyses.

Methods. Spectra have been reduced and extracted with a dedicated pipeline that uses photometric information from deep CFHT legacy survey (CFHT-LS) reference images to trace, at sub-pixel accuracy, the position of the supernova on the spectrogram as a function of wavelength. It also separates the supernova and its host light in ~60% of cases. The identification of the supernova candidates is performed using a spectrophotometric SN Ia model.

Results. A total of 124 SNe Ia, roughly 50% of the overall SNLS spectroscopic sample, have been identified using the ESO/VLT during the first three years of the survey. Their redshifts range from to . The average redshift of the sample is z = 0.63±0.02. This constitutes the largest SN Ia spectral set to date in this redshift range. The spectra are presented along with their best-fit spectral SN Ia model and a host model where relevant. In the latter case, a host subtracted spectrum is also presented. We produce average spectra for pre-maximum, maximum and post-maximum epochs for both and z ≥ 0.5 SNe Ia. We find that spectra have deeper intermediate mass element absorptions than z ≥ 0.5 spectra. The differences with redshift are consistent with the selection of brighter and bluer supernovae at higher redshift.