Quantitative comparison between type Ia supernova spectra at low and high redshifts: a case study

¹ Department of Physics, Stockholm University, Albanova University Center, 106 91 Stockholm, Sweden e-mail: gabri@physto.se
² LPNHE, CNRS-IN2P3, University of Paris VI & VII, Paris, France
³ Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA 91101, USA
⁴ E. O. Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, USA
⁵ Osservatorio Astronomico di Padova, INAF, vicolo dell'Osservatorio 5, 35122 Padova, Italy
⁶ Department of Physics, University of Oxford, Nuclear & Astrophysics Laboratory, Keble Road, Oxford OX1 3RH, UK
⁷ Colorado College, 14 East Cache La Poudre St., Colorado Springs, CO 80903
⁸ Department of Physics, University of California Berkeley, Berkeley, 94720-7300 CA, USA
⁹ American Astronomical Society, 2000 Florida Ave, NW, Suite 400, Washington, DC, 20009 USA
¹⁰ Institute of Astronomy, School of Science, University of Tokyo, Mitaka, Tokyo 181-0015, Japan
¹¹ CENTRA e Dep. de Fisica, IST, Univ. Tecnica de Lisboa
¹² Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37240, USA
¹³ Department of Astronomy and Astrophysics, University of Toronto, 60 St. George St., Toronto, Ontario M5S 3H8, Canada
¹⁴ National Astronomical Observatory, Mitaka, Tokyo 181-0058, Japan
¹⁵ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
¹⁶ Isaac Newton Group, Apartado de Correos 321, 38780 Santa Cruz de La Palma, Islas Canarias, Spain
¹⁷ Department of Astronomy, University of Barcelona, Barcelona, Spain
¹⁸ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
¹⁹ Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, 277 8582 Japan

Received: 10 April 2006
Accepted: 21 March 2007

Abstract

We develop a method to measure the strength of the absorption features in type Ia supernova (SN Ia) spectra and use it to make a quantitative comparisons between the spectra of type Ia supernovae at low and high redshifts. In this case study, we apply the method to 12 high-redshift (0.212 ≤ z ≤ 0.912) SNe Ia observed by the Supernova Cosmology Project. Through measurements of the strengths of these features and of the blueshift of the absorption minimum in Ca ii H&K, we show that the spectra of the high-redshift SNe Ia are quantitatively similar to spectra of nearby SNe Ia (z < 0.15). One supernova in our high redshift sample, SN 2002fd at z = 0.279, is found to have spectral characteristics that are associated with peculiar SN 1991T/SN 1999aa-like supernovae.