Browsing by Author "Kasai, Eli Kunwiji"

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    SALT spectroscopy and classification of supernova spectra using Bayesian techniques
    (2017) Kasai, Eli Kunwiji; Bassett, Bruce A; Crawford Steven, M
    In this thesis, we present the Southern African Large Telescope spectroscopic follow-up programme for supernova candidates discovered by the international Dark Energy Survey, the goals of which are to measure the expansion history of the Universe and shed light on the mysterious nature of dark energy. In total, we took spectra for 36 supernova candidates. These were classified using a new Bayesian Supernova spectra classifier, SuperNovaMC, that we developed to address limitations with existing algorithms. SuperNovaMC simultaneously finds the best fitting supernova and host galaxy using Bayesian model selection, fitting the entire spectrum with Monte Carlo Markov Chain methods which allow estimation of the entire parameter posterior distributions, and hence principled statistical analysis even at low signal-to-noise. After extensive testing of SuperNovaMC against simulations and literature data, we use it to classify 20 of our Dark Energy Survey candidates as Type Ia supernovae. We further performed equivalent width measurements of two Type Ia supernova spectral features: Ca II H&K and Si II 4000, using a sub-sample of the 20 Type Ia supernovae. We compared our results to those of a similar study conducted on a low-redshift (z < 0:1) Type Ia supernova sample and found the two sets of results to be consistent, suggesting no redshift evolution in the equivalent widths of the two spectral features in the redshift range 0:1 < z < 0:3 that we conducted the study in.
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    The type IA supernova rate in intermediate redshift galaxy clusters
    (2013) Kasai, Eli Kunwiji; Crawford, Steve; Bassett, Bruce A
    Studies of Type Ia supernovae (SNe Ia) in galaxy clusters can tell us about the metal enrichment of the intra-cluster medium, constrain the star formation history of cluster galaxies, aid us in the investigations of the progenitor systems of SNe Ia, act as tracers of the intra-cluster stellar population and can be used in measuring distances over extragalactic scales, which is relevant to supernova cosmology. However, the value of the cluster Type Ia supernova (SN Ia) rate at intermediate redshifts has not been well constrained and this hampers our ability to derive accurately the parameters needed in addressing the topics listed above. We have performed a search for supernovae and other transients in six galaxy clusters, located in the redshift range 0:3 < z < 0:9 to derive the cluster Type Ia supernova (SN Ia) rate.