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Limiting the dimming of distant type Ia supernovae
Stockholm University, Faculty of Science, Department of Physics. (CoPS)
Stockholm University, Faculty of Science, Department of Physics. (CoPS)
2005 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, no 2, 5- p.Article in journal (Refereed) Published
Abstract [en]

Distant supernovae have been observed to be fainter than what is expected in a matter dominated universe. The most likely explanation is that the universe is dominated by an energy component with negative pressure, namely dark energy. However, there are several astrophysical processes that could, in principle, affect the measurements and in order to be able to take advantage of the growing supernova statistics, the control of systematic effects is crucial. We discuss two of these; extinction due to intergalactic grey dust and dimming due to photon-axion oscillations and show how their effect on supernova observations can be constrained using observed quasar colours and spectra. For a wide range of intergalactic dust models, we are able to rule out any dimming larger than 0.2 magnitudes for a type Ia supernova at z = 1. The corresponding limit for intergalactic Milky Way type dust is 0.03 magnitudes. For the more speculative model of photons mixing with axions, we find that the effect is independent of photon energy for certain combinations of parameter values and a dimming as large as 0.6 magnitudes cannot be ruled out. These effects can have profound implications for the possibility of constraining dark energy properties using supernova observations.

Place, publisher, year, edition, pages
2005. no 2, 5- p.
Keyword [en]
Type Ia supernovae, quasars, cosmology, axions, dust, intergalactic medium
National Category
Astronomy, Astrophysics and Cosmology Astronomy, Astrophysics and Cosmology
Research subject
URN: urn:nbn:se:su:diva-29516DOI: 10.1088/1475-7516/2005/02/005OAI: diva2:233890
Available from: 2009-09-03 Created: 2009-09-03 Last updated: 2009-09-07Bibliographically 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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