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Properties of Type Ia supernova spectra up to z ~0.3
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Context: Distance estimates using Type Ia supernovae lead to the discovery of the accelerating universe a decade ago. Further high precision studies of the dynamics of the universe using supernovae are now limited by systematic uncertainties. Optical spectra of supernovae from follow-up observations of the SDSS-II Supernova Survey provide a natural testbed for investigating key uncertainties like a potential brightness evolution of the standard candle and the nature of the observed non-standard colour-brightness relation. Spectroscopic data also provides information needed to improve our understanding of the physical processes taking place in Type Ia supernova explosions.

Aims: If supernova properties change with redshift, this may be detectable through comparisons of spectral indicators. Studies of individual supernovae are needed in order to determine whether explosionproperties, and not only the population distribution, change with redshift. Similarly, a possible intrinsic colour-brightness relation can be explored through correlations with spectral properties.Methods: We describe spectral indicator studies of spectra observed at the NTT and NOT during 2006 and 2007. These benefit from excellent multi-band SDSS photometry while being at cosmological distances (z=0.05-0.3) where evolution, limiting Type Ia supernovae as standarizable candles, could be present. We perform measurements of pseudo equivalent widths and line velocities as a function of redshift and lightcurve parameters. We also present multiple Monte Carlo studies designed to determine possible systematic errors in our spectral analysis arising when comparing local high S/N supernova spectra with lower S/N host-contaminated distant spectra.Reults: We do not detect any significant signs of evolution in individual Type Ia supernova spectra up to z=0.3. Better control of selection effects (both of the local and the distant sample) is needed in orderto determine whether a population drift exists. We can confirm correlations between pseudo equivalent widths and lightcurve shape (stretch) and see indications of correlations with supernova colours. We conclude that it is possible to compare individual low S/N supernova spectra with local ones, but that care must be taken during both noise filtering and host-galaxy subtraction.  Host-galaxy contamination is the single largest source of systematic errors in our study, especially in the presence of differential slit loss.

URN: urn:nbn:se:su:diva-29548OAI: diva2:234107
Available from: 2009-09-04 Created: 2009-09-04 Last updated: 2010-01-14Bibliographically approved
In thesis
1. Extragalactic extinction and spectral properties of Type Ia supernovae
Open this publication in new window or tab >>Extragalactic extinction and spectral properties of Type Ia supernovae
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of Type Ia supernovae as standardisable candles for probing cosmological parameters with high precision requires good knowledge about how the supernova light is affected along the line of sight and how the intrinsic brightness varies between objects. The work in this thesis addresses these topics.

One potential problem is if there is an evolution of the intrinsic brightness of Type Ia supernovae with redshift. To investigate this we have compared spectral features of intermediate-redshift supernovae with local ones. No redshift evolution could be detected up to z = 0.3. Correlations of the strength of some of the spectral features with supernova colour and lightcurve shape were found, in particular for the feature which primarily is a product of SiII 4130 absorption.

Another difficulty concerns dust present in the line of sight which could both dim and redden the supernovae. We investigated dust extinction in distant galaxies by comparing the colours of background quasars with what is expected for different types of dust. A wide range of fitted values of Rv, the total-to-selective extinction ratio, was found, indicating that the dust properties in other galaxies could potentially be different from the Milky Way value, Rv ~ 3.1.

The light could also be affected by an intergalactic dust population with an almost flat extinction curve. We found, using quasar observations, that any dimming larger than 0.2 magnitudes in the rest-frame B-band for a Type Ia supernova at z = 1 is ruled out. If the intergalactic dust has an extinction law similar to the one in the Milky Way, the corresponding limit would be 0.03 magnitudes.

Another problem is that if axions exist, photons could be converted to axions over large cosmological distances, in the presence of magnetic fields, leading to a dimming of distant objects. For some model parameters, a dimming as large as 0.6 magnitudes for a Type Ia supernova at z = 1 would be allowed from quasar observations.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2009. 112 p.
Type Ia supernovae, cosmology, spectroscopy, dust extinction, quasars, axions
National Category
Physical Sciences
Research subject
urn:nbn:se:su:diva-29521 (URN)978-91-7155-912-8 (ISBN)
Public defence
2009-10-02, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: In progress. Paper 5: In progress.Available from: 2009-09-10 Created: 2009-09-03 Last updated: 2011-04-27Bibliographically approved

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Nordin, JakobÖstman, LindaAmanullah, RahmanGoobar, Ariel
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