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The Discovery and Classification of 16 Supernovae at High Redshifts in ELAIS-S1: the Stockholm VIMOS Supernova Survey II
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). (Galaxer och kosmologi)
Space Telescope Science Institute.
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). (Galaxer och kosmologi)
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(English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed) Submitted
Abstract [en]

Supernova surveys can be used to study a variety of subjects, such as: (i) cosmology using type Ia supernovae, (ii) star formationrates using core-collapse SNe, (iii) supernova properties and their connection to host galaxy characteristics. The Stockholm VIMOSSupernova Survey (SVISS) is a multi-band imaging survey aiming to detect supernovae at redshift 0.5 and derive thermonuclearand core-collapse supernova rates at high redshift. In this paper we present the supernovae discovered in the survey along with lightcurves and a photometric classification into thermonuclear and core-collapse types. To detect the supernovae in the VLT/VIMOSmulti-epoch images we used difference imaging and a combination of automatic and manual source detection to minimise the numberof spurious detections. Photometry for the found variable sources was obtained and careful simulations done to estimate correct errors.The light curves were typed using a Bayesian probability method and Monte Carlo simulations were used to study misclassification.We detected 16 supernovae, eight of which had a core-collapse origin and eight that had a thermonuclear origin. The estimatedmisclassification errors are quite small, on the order of 5%, but vary with both redshift and type. The mean redshift of the supernovaeis 0.64. Additionally, we found a variable source with a very extended light curve that could possibly be a pair instability supernova.

Keyword [en]
supernovae, supernova typing
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-56778OAI: oai:DiVA.org:su-56778DiVA: diva2:413071
Available from: 2011-04-27 Created: 2011-04-27 Last updated: 2011-09-15Bibliographically 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.
Keyword
supernovae, supernova typing, supernova rates, photometric redshifts, Lyman Break Galaxies
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
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)
Opponent
Supervisors
Note
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
2. Distant supernovae and galaxies in the Stockholm VIMOS Supernova Survey
Open this publication in new window or tab >>Distant supernovae and galaxies in the Stockholm VIMOS Supernova Survey
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Multi colour imaging surveys help astronomers to find galaxies and clusters,and to gain insights on their physical properties and evolution.

In this thesis, I present the Stockholm VIMOS Supernova Survey (SVISS), where the ELAIS-S field was observed with VIMOS UBVRI broad-band optical bands over a period of 5 years. The main goal of SVISS is to determine supernova rates at redshifts from z~0.1-1, but the wealth of data enable us to study also galaxy evolution and the supernovae hosts galaxies. I describe the work done to create a deep photometric catalogue of galaxies in the field,including computations of survey completeness and galaxy number counts. In addition I describehow we use colour criteria to select high redshift galaxy candidates (so called Lyman Break Galaxies).Photometric redshifts have been obtained for most galaxies in the field using a template-fitting method. I briefly describe this method and present the resulting redshift distribution.

We have found 16 supernovae in total, 7 thermonuclear supernovae and 9 core collapse, using the difference imaging technique.From their broad band flux and colour evolution of the supernovae, we classified them into core collapse and thermonuclear supernovae, with an internal accuracy of 95%. We compute supernova rates for both types up to redshift of 1, and we show a good agreement with the other determined rates.

We have done studies on the relation between supernovae and host galaxies to try understand the nature of supernovae and their environments.The position of the supernovae within the galaxies, their star formation rate, host galaxy luminosity, among others, have been derived and tested against published results showing a good agreement with results at lower redshifts.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2011. 80 p.
Keyword
imaging surveys, photometric redshfits, Lyman Break galaxies, supernova typing, supernova rates, supernova host galaxies
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-62118 (URN)978-91-7447-362-9 (ISBN)
Public defence
2011-10-10, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 2: Submitted. Paper 3: Manuscript. Paper 4: Manuscript.Available from: 2011-09-18 Created: 2011-09-09 Last updated: 2011-09-15Bibliographically approved

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