A&A 466, 11-21 (2007)
DOI: 10.1051/0004-6361:20066930

SALT2: using distant supernovae to improve the use of type Ia supernovae as distance indicators

J. Guy¹, P. Astier¹, S. Baumont¹, D. Hardin¹, R. Pain¹, N. Regnault¹, S. Basa², R. G. Carlberg³, A. Conley³, S. Fabbro⁴, D. Fouchez⁵, I. M. Hook⁶, D. A. Howell³, K. Perrett³, C. J. Pritchet⁷, J. Rich⁸, M. Sullivan³, P. Antilogus¹, E. Aubourg⁸, G. Bazin⁸, J. Bronder⁶, M. Filiol², N. Palanque-Delabrouille⁸, P. Ripoche⁵, and V. Ruhlmann-Kleider<sup>8

1</sup>  LPNHE, CNRS-IN2P3 and Universités Paris VI & VII, 4 place Jussieu, 75252 Paris Cedex 05, France
    e-mail: guy@in2p3.fr
²  LAM, CNRS, BP 8, Traverse du Siphon, 13376 Marseille Cedex 12, France
³  Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H8, Canada
⁴  CENTRA-Centro M. de Astrofisica and Department of Physics, IST, Lisbon, Portugal
⁵  CPPM, CNRS-IN2P3 and Université Aix-Marseille II, Case 907, 13288 Marseille Cedex 9, France
⁶  University of Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁷  Department of Physics and Astronomy, University of Victoria, PO Box 3055, Victoria, BC VSW 3P6, Canada
⁸  DSM/DAPNIA, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France

(Received 13 December 2006 / Accepted 30 January 2007 )

Abstract
Aims.We present an empirical model of type Ia supernovae spectro-photometric evolution with time.
Methods.The model is built using a large data set including light-curves and spectra of both nearby and distant supernovae, the latter being observed by the SNLS collaboration. We derive the average spectral sequence of type Ia supernovae and their main variability components including a color variation law. The model allows us to measure distance moduli in the spectral range with calculable uncertainties, including those arising from variability of spectral features.
Results.Thanks to the use of high-redshift SNe to model the rest-frame UV spectral energy distribution, we are able to derive improved distance estimates for SNe Ia in the redshift range 0.8<z<1.1. The model can also be used to improve spectroscopic identification algorithms, and derive photometric redshifts of distant type Ia supernovae.

Key words: supernovae: general -- cosmology: observations

© ESO 2007

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