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Detection efficiency and photometry in supernova surveys: The Stockholm VIMOS Supernova Survey I
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
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2008 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 490, no 1, 419-434 p.Article in journal (Refereed) Published
Abstract [en]

Aims. The aim of the work presented in this paper is to test and optimise supernova detection methods based on the optimal image subtraction technique. The main focus is on applying the detection methods to wide field supernova imaging surveys and in particular to the Stockholm VIMOS Supernova Survey (SVISS).

Methods. We have constructed a supernova detection pipeline for imaging surveys. The core of the pipeline is image subtraction using the ISIS 2.2 package. Using real data from the SVISS we simulate supernovae in the images, both inside and outside galaxies. The detection pipeline is then run on the simulated frames and the effects of image quality and subtraction parameters on the detection efficiency and photometric accuracy are studied.

Results. The pipeline allows efficient detection of faint supernovae in the deep imaging data. It also allows controlling and correcting for possible systematic effects in the SN detection and photometry. We find such a systematic effect in the form of a small systematic flux offset remaining at the positions of galaxies in the subtracted frames. This offset will not only affect the photometric accuracy of

the survey, but also the detection efficiencies.

Conclusions. Our study has shown that ISIS 2.2 works well for the SVISS data. We have found that the detection efficiency and

photometric accuracy of the survey are affected by the stamp selection for the image subtraction and by host galaxy brightness. With our tools the subtraction results can be further optimised, any systematic effects can be controlled and photometric errors estimated, which is very important for the SVISS, as well as for future SN searches based on large imaging surveys such as Pan-STARRS and LSST.

Place, publisher, year, edition, pages
2008. Vol. 490, no 1, 419-434 p.
Keyword [en]
supernovae: general, methods: data analysis, surveys
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-14680DOI: doi:10.1051/0004-6361:20079206OAI: diva2:181200
Available from: 2008-10-23 Created: 2008-10-23 Last updated: 2011-04-27Bibliographically approved
In thesis
1. The Frequency of Supernovae in the Early Universe
Open this publication in new window or tab >>The Frequency of Supernovae in the Early Universe
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2011. 55 p.
supernovae, supernova typing, supernova rates, photometric redshifts, Lyman Break Galaxies
National Category
Astronomy, Astrophysics and Cosmology
Research subject
urn:nbn:se:su:diva-56000 (URN)978-91-7447-274-5 (ISBN)
Public defence
2011-05-20, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript. Paper 4: Manuscript.Available from: 2011-04-28 Created: 2011-04-04 Last updated: 2011-04-27Bibliographically approved

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