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Quantifying Systematic Uncertainties in Supernova Cosmology
Stockholm University, Faculty of Science, Department of Physics. (COPS)
Stockholm University, Faculty of Science, Department of Physics. (COPS)
Stockholm University, Faculty of Science, Department of Physics. (COPS)
2008 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, Vol. 02, 008- p.Article in journal (Refereed) Published
Abstract [en]

Observations of Type Ia supernovae used to map the expansion history of the Universe suffer from systematic uncertainties that need to be propagated into the estimates of cosmological parameters. We propose an iterative Monte Carlo simulation and cosmology fitting technique (SMOCK) to investigate the impact of sources of error upon fits of the dark energy equation of state. This approach is especially useful to track the impact of non-Gaussian, correlated effects, e.g. reddening correction errors, brightness evolution of the supernovae, K-corrections, gravitational lensing, etc. While the tool is primarily aimed at studies and optimization of future instruments, we use the Gold data-set in Riess et al (2007 Astrophys. J. 659 98) to show examples of potential systematic uncertainties that could exceed the quoted statistical uncertainties.

Place, publisher, year, edition, pages
2008. Vol. 02, 008- p.
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-16774DOI: 10.1088/1475-7516/2008/02/008ISI: 000254151100008OAI: oai:DiVA.org:su-16774DiVA: diva2:183294
Available from: 2008-12-23 Created: 2008-12-23 Last updated: 2011-04-27Bibliographically approved
In thesis
1. Spectral Properties of Type Ia Supernovae and Implications for Cosmology
Open this publication in new window or tab >>Spectral Properties of Type Ia Supernovae and Implications for Cosmology
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Type Ia supernovae can, for a short period of time, reach the same brightness as an entire galaxy. They are responsible for the creation of a large fraction of all heavy elements and can be used, as standard candles, to prove that the expansion of the universe is accelerating. Yet, we do not fully understand them.

A basic picture where Type Ia supernovae are caused by thermonuclear explosions of white dwarfs is generally accepted, but the details are still debated. These unknowns propagate into systematic uncertainties in the estimates of cosmological parameters. A Monte Carlo framework, SMOCK, designed to model this error propagation, is presented. Evolution with time/distance and the nature of reddening are studied as the dominant astrophysical uncertainties.

Optical spectra of Type Ia supernovae contain a wealth of information regarding the nature of these events, and can be used both to understand supernovae and to limit the systematic uncertainties in cosmological parameter estimates. We have reduced spectra observed with the Nordic Optical Telescope and the New Technology Telescope in conjunction with the SDSS-II supernova survey, and compared spectral properties (pseudo-Equivalent Widths and line velocities) of this sample with local supernovae.We have further studied possible systematic difficulties in such comparisons between nearby and distant supernovae, caused by noise and host galaxy contamination.Taking such uncertainties into account, we find a tentative evolution in supernova properties with redshift, compatible with expected demographic changes. Correlations with light curve shape found by other studies are confirmed. A tentative correlation with light curve colour is also presented. The latter could indicate an intrinsic component of the observed reddening, i.e. independent of interstellar dust in the host galaxy.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2011. 81 p.
Keyword
cosmology, spectroscopy, supernovae
National Category
Physical Sciences Astronomy, Astrophysics and Cosmology Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-56785 (URN)978-91-7447-300-1 (ISBN)
Public defence
2011-05-27, lecture room FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Accepted. Available from: 2011-05-05 Created: 2011-04-27 Last updated: 2011-04-29Bibliographically approved

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