Restframe I-band Hubble diagram for type Ia supernovae up to redshift z 0.5

¹ LPNHE, CNRS-IN2P3, University of Paris VI & VII, Paris, France e-mail: serena@lpnhep.in2p3.fr
² Department of Physics, Stockholm University, Albanova University Center, 106 91 Stockholm, Sweden
³ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
⁴ E. O. Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, USA
⁵ Colorado College, 14 East Cache La Poudre St., Colorado Springs, CO 80903, USA
⁶ Department of Physics, University of California Berkeley, Berkeley, 94720-7300 CA, USA
⁷ American Astronomical Society, 2000 Florida Ave, NW, Suite 400, Washington, DC, 20009 USA
⁸ California Institute of Technology, E. California Blvd, Pasadena, CA 91125, USA
⁹ CENTRA-Centro M. de Astrofísica and Department of Physics, IST, Lisbon, Portugal
¹⁰ Department of Physics, University of Oxford, Nuclear & Astrophysics Laboratory, Keble Road, Oxford, OX1 3RH, UK
¹¹ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37240, USA
¹² Department of Astronomy, University of Barcelona, Barcelona, Spain

Received: 1 December 2004
Accepted: 1 April 2005

Abstract

We present a novel technique for fitting restframe I-band light curves on a data set of 42 type Ia supernovae (SNe Ia). Using the result of the fit, we construct a Hubble diagram with 26 SNe from the subset at . Adding two SNe at yields results consistent with a flat Λ-dominated “concordance universe” () = (0.25, 0.75). For one of these, SN 2000fr, new near infrared data are presented. The high redshift supernova NIR data are also used to test for systematic effects in the use of SNe Ia as distance estimators. A flat, , universe where the faintness of supernovae at is due to grey dust homogeneously distributed in the intergalactic medium is disfavoured based on the high-z Hubble diagram using this small data-set. However, the uncertainties are large and no firm conclusion may be drawn. We explore the possibility of setting limits on intergalactic dust based on and  colour measurements, and conclude that about 20 well measured SNe are needed to give statistically significant results. We also show that the high redshift restframe I-band data points are better fit by light curve templates that show a prominent second peak, suggesting that they are not intrinsically underluminous.