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- Melinder, Jens, 1977-
(författare)
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The Frequency of Supernovae in the Early Universe
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Supernovae are cosmic explosions of cataclysmic proportion that signify the death of a star. While being interesting phenomena in their own right, their brightness also make them excellent probes of the early universe. Depending on the type of the progenitor star and the origin of the explosion different subjects can be investigated. In this dissertation the work I have done on the detection, characterisation and rate measurements of supernovae in the Stockholm VIMOS Supernova Search is presented. We have discovered 16 supernovae that exploded billions of years ago (or, equivalently, at high redshift, z). The observed brightness and colour evolution have been used to classify the supernovae into either thermonuclear (type Ia) or core collapse (type II) supernovae. The accuracy of the classification code is high, only about 5% of the supernovae are mistyped, similar to other codes of the same kind. By comparing the observed frequency of supernovae to simulations the underlying supernova rate at these high redshifts have been measured. The main result reported in this thesis is that the core collapse supernova rate at high redshift matches the rates estimated from looking at the star formation history of the universe, and agree well with previous studies. The rate of Ia supernovae at high redshift have been investigated by several projects, our results show a somewhat higher rate of Ia supernovae than expected. Proper estimates of the systematic errors of rate measurements are found to be very important. Furthermore, by using novel techniques for reducing and stacking images, we have obtained a galaxy sample containing approximately 50,000 galaxies. Photometric redshifts have been obtained for most of the galaxies, the resulting accuracy below z=1 is on the order of 10%. The galaxy sample has also been used to find high redshift sources, so called Lyman Break Galaxies, at z=3-5.
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| 2. |
- Melinder, Jens, 1977-, et al.
(författare)
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The Rate of Supernovae at Redshift 0.1 − 1.0 : the Stockholm VIMOS Supernova Survey IV
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 545:A96
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present supernova rate measurements at redshift 0.1–1.5 from the Stockholm VIMOS Supernova Survey (SVISS). The sample contains 16 supernovae in total. The discovered supernovae have been classified into core collapse or thermonuclear (Ia) types based on their light curves, colour evolution and host galaxy photometric redshift. The rates we find for the core collapse supernovae are 1.25 (+2.27 +0.85 −0.97 −0.78) - with statistical and systematic errors, respectively - at z = 0.39 and 6.90 (+5.24 +3.04 −3.25 −2.14) at z = 0.73. For the Ia supernovae the rates are 2.02 (+1.57 +0.53−0.96 −0.57) at z = 0.39 and 1.03 (+0.92 +0.31−0.54 −0.36) at z = 0.80. All of these rate estimates have been corrected for host galaxy extinction. Using Monte Carlo simulations we make a thorough study of the systematic effects from assumptions made when calculating the rates and find that the most important errors comes from misclassification, the assumed mix of faint and bright supernova types and uncertainties in redshift. We compare our rates to other observations, to the star formation history for core collapse rates and to different models of the delay time distribution for Ia rates. Overall, our measurements agree quite well with these other rates when using redshift-dependent corrections for extinction. We do not find any evidence of a missing fraction of core collapse supernovae.
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