Photometric redshifts for type Ia supernovae in the supernova legacy survey

¹ CEA, Centre de Saclay, Irfu/SPP, 91191 Gif-sur-Yvette, France e-mail: nathalie.palanque-delabrouille@cea.fr
² LPNHE, Université Pierre et Marie Curie, Université Paris diderot, CNRS-IN2P3, 4 place Jussieu, 75252 Paris Cedex 05, France
³ University Paris 11, 91405 Orsay, France
⁴ LAM, CNRS, BP8, Pôle de l'étoile, Site de Château-Gombert, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁵ Deparment of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H8, Canada
⁶ Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389, USA
⁷ CPPM, CNRS-Luminy, Case 907, 13288 Marseille Cedex 9, France
⁸ Department of Physics (Astrophysics), University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁹ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio (RM), Italy
¹⁰ Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102, Goleta, CA 93117, USA
¹¹ Department of Physics, University of California, Santa Barbara, Broida Hall, Mail Code 9530, Santa Barbara, CA 93106-9530, USA
¹² Department of Physics and Astronomy, University of Victoria, PO Box 3055, Victoria, BC V8W 3P6, Canada

Received: 11 September 2009
Accepted: 15 February 2010

Abstract

We present a method using the SALT2 light curve fitter to determine the redshift of type Ia supernovae in the Supernova Legacy Survey (SNLS) based on their photometry in g', r', i' and z'. On 289 supernovae of the first three years of SNLS data, we obtain a precision = 0.022 on average up to a redshift of 1.0, with a higher precision of 0.016 for z < 0.45 and a lower one of 0.025 for z > 0.45. The rate of events with |Δ z|/(1+z) > 0.15 (catastrophic errors) is 1.4%, and reduces to 0.4% when restricting the test sample of spectroscopically confirmed Type Ia supernovae. Both the precision and the rate of catastrophic errors are better than what can be currently obtained using host galaxy photometric redshifts. Photometric redshifts of this precision may be useful for future experiments which aim to discover up to millions of supernovae Ia but without spectroscopy for most of them.