Using line profiles to test the fraternity of type Ia supernovae at high and low redshifts

Stéphane Blondin*, Luc Dessart, Bruno Leibundgut, David Branch, Peter Höflich, John L. Tonry, Thomas Matheson, Ryan J. Foley, Ryan Chornock, Alexei V. Filippenko, Jesper Sollerman, Jason Spyromilio, Robert P. Kirshner, W. Michael Wood-Vasey, Alejandro Clocchiatti, Claudio Aguilera, Brian Barris, Andrew C. Becker, Peter Challis, Ricardo CovarrubiasTamara M. Davis, Peter Garnavich, Malcolm Hicken, Saurabh Jha, Kevin Krisciunas, L. I. Weidong, Anthony Miceli, Gajus Miknaitis, Giuliano Pignata, Jose Luis Prieto, Armin Rest, Adam G. Riess, Maria Elena Salvo, Brian P. Schmidt, R. Chris Smith, Christopher W. Stubbs, Nicholas B. Suntzeff

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

82 Scopus citations


Using archival data of low-redshift (z < 0.01; Center for Astrophysics and SUSPECT databases) Type Ia supernovae (SNe Ia) and recent observations of high-redshift (0.16 < z < 0.64) SNe Ia, we study the "uniformity" of the spectroscopic properties of nearby and distant SNe Ia. We find no difference in the measurements we describe here. In this paper we base our analysis solely on line-profile morphology, focusing on measurements of the velocity location of maximum absorption (v abs) and peak emission (v peak). Our measurement technique makes it easier to compare low and high signal-to-noise ratio observations. We also quantify the associated sources of error, assessing the effect of line blending with assistance from the parameterized code SYNOW. We find that the evolution of v abs and v peak for our sample lines (Ca II λ3945, Si II λ6355, and S II λλ5454, 5640) is similar for both the low- and high-redshift samples. We find that v abs for the weak S II λλ5454, 5640 lines and v peak for S II λ5454 can be used to identify fast-declining [Δm 15(B) > 1.7] SNe Ia, which are also subluminous. In addition, we give the first direct evidence in two high-z SN Ia spectra of a double-absorption feature in Ca II λ3945, an event also observed, although infrequently, in low-redshift SN Ia spectra (6 out of 22 SNe Ia in our local sample). Moreover, echoing the recent studies of Dessart & Hillier in the context of Type II supernovae (SNe II), we see similar P Cygni line profiles in our large sample of SN Ia spectra. First, the magnitude of the velocity location at maximum profile absorption may underestimate that at the continuum photosphere, as observed, for example, in the optically thinner line S II λ5640. Second, we report for the first time the unambiguous and systematic intrinsic blueshift of peak emission of optical P Cygni line profiles in SN Ia spectra, by as much as 8000 km s -1. All the high-z SNe Ia analyzed in this paper were discovered and followed up by the ESSENCE collaboration and are now publicly available.

Original languageEnglish (US)
Pages (from-to)1648-1666
Number of pages19
JournalAstronomical Journal
Issue number3
StatePublished - Mar 2006


  • Cosmology: observations
  • Line: formation
  • Line: profiles
  • Supernovae: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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