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Published January 2008 | Published + Submitted
Journal Article Open

SNLS spectroscopy: testing for evolution in type Ia supernovae


Aims. We present a quantitative study of a new data set of high redshift Type Ia supernovae spectra, observed at the Gemini telescopes during the first 34 months of the Supernova Legacy Survey. During this time 123 supernovae candidates were observed, of which 87 have been identified as SNe Ia at a median redshift of z=0.720. Spectra from the entire second year of the survey and part of the third year (59 total SNe candidates with 46 confirmed SNe Ia) are published here for the first time. The spectroscopic measurements made on this data set are used determine if these distant SNe comprise a population similar to those observed locally. Methods. Rest-frame equivalent width and ejection velocity measurements are made on four spectroscopic features. Corresponding measurements are presented for a set of 167 spectra from 24 low-z SNe Ia from the literature. Results. We show that there exists a sample at high redshift with properties similar to nearby SNe. The high-z measurements are consistent with the range of measurements at low-z and no significant difference was found between the distributions of measurements at low and high redsift for three of the features. The fourth feature displays a possible difference that should be investigated further. Correlations between Type Ia SNe properties and host galaxy morphology were also found to be similar at low and high z, and within each host galaxy class we see no evidence for redshift-evolution in SN properties. A new correlation between SNe Ia peak magnitude and the equivalent width of SiII absorption is presented. Tests on a sub-set of the SNLS SNe demonstrates that this correlation reduces the scatter in SNe Ia luminosity distances in a manner consistent with the lightcurve shape-luminosity corrections that are used for Type Ia SNe cosmology. Conclusions. We show that this new sample of SNLS SNe Ia has spectroscopic properties similar to nearby objects.

Additional Information

© ESO 2008. (Received 16 April 2007 / Accepted 31 July 2007) The SNLS collaboration gratefully acknowledges the assistance of Pierre Martin and the CFHT Queued Service Observations team. We also thank the Gemini queue observers and support staff for both taking the data presented in this paper and making observations available quickly. T.J.B. is grateful to Exeter College and the Alberta-Bart Holaday Scholarship. T.J.B. would also like to thank the EU Type Ia SNe RTN "young researchers'' - particularly Gabriele Garavini and Gaston Folatelli - for all of their assistance. Canadian collaboration members acknowledge support from NSERC and CIAR; French collaboration members from CNRS/IN2P3, CNRS/INSU and CEA; Portuguese Collaboration members acknowledge support from FCT-Fundacao para a Ciencia e Tecnologia; UK collaborators acknowledge support from the Science and Technolgy Facilities Council (STFC, formerly PPARC). SNLS relies on observations with MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope which is operated by the National Research Council of Candada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. This work is based in part on data products produced at the Canadian Astronomy Data Centre as part of the CFHT Legacy Survey, a collaborative project of the National Research Council of Canada and the French Centre national de la recherche scientifique. The Work is also based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the STFC (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil) and CONICET (Argentina). This research used observations from Gemini program numbers: GN-2005A-Q-11, GN-2005B-Q-7, GN-2006A-Q-7, GS-2005A-Q-11 and GS-2005B-Q-6. The views expressed in this article are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the US Government.

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