Change search
ReferencesLink to record
Permanent link

Direct link
The Frequency of Supernovae in the Early Universe
Stockholm University, Faculty of Science, Department of Astronomy. (Galaxer och kosmologi)
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 [en]
supernovae, supernova typing, supernova rates, photometric redshifts, Lyman Break Galaxies
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-56000ISBN: 978-91-7447-274-5OAI: oai:DiVA.org:su-56000DiVA: diva2:410152
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
List of papers
1. Detection efficiency and photometry in supernova surveys: The Stockholm VIMOS Supernova Survey I
Open this publication in new window or tab >>Detection efficiency and photometry in supernova surveys: The Stockholm VIMOS Supernova Survey I
Show others...
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.

Keyword
supernovae: general, methods: data analysis, surveys
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-14680 (URN)doi:10.1051/0004-6361:20079206 (DOI)
Available from: 2008-10-23 Created: 2008-10-23 Last updated: 2011-04-27Bibliographically approved
2. The Discovery and Classification of 16 Supernovae at High Redshifts in ELAIS-S1: the Stockholm VIMOS Supernova Survey II
Open this publication in new window or tab >>The Discovery and Classification of 16 Supernovae at High Redshifts in ELAIS-S1: the Stockholm VIMOS Supernova Survey II
Show others...
(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
supernovae, supernova typing
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-56778 (URN)
Available from: 2011-04-27 Created: 2011-04-27 Last updated: 2011-09-15Bibliographically approved
3. Deep UBVRI observations of a field within ELAIS-S1: the Stockholm VIMOS Supernova Survey III
Open this publication in new window or tab >>Deep UBVRI observations of a field within ELAIS-S1: the Stockholm VIMOS Supernova Survey III
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Context. The Stockholm VIMOS Supernova Survey (SVISS) is an optical broad-band photometry survey, aimed at the search fordistant (redshifts z~0.7) supernovae, which are detected by means of monthly imaging in R and I bands with the VIMOS instrumenton the ESO VLT. The distances of the supernovae are estimated using photometric redshifts facilitated by additional U, B and V imaging also with VIMOS. In this paper we present the deep stacked imaging data in all these bands and a catalogue of galaxiesextending to very faint magnitudes.

Aims. We discuss the various steps followed to create a galaxy catalog, including the reduction and stacking of the data, astrometricand photometric calibration and source detections.We derived completeness, corrected number counts and color selected Lyman breakgalaxies. Raw number counts are also calculated. Finally, making use of a template fitting code, photometric redshifts are derived.

Methods. UBVRI deep imaging of a 4x56 sq. arcmin field within the ELAIS-S1 field is presented in this paper. The data reduction has been done with a dedicated MIDAS pipeline. The final images have been weighted by their seeing, which was found to optimise depth and spatial resolution. Source detection and phortometry was done using SExtractor. The photometric accuracy was tested by comparing the colors of the sources to stellar libraries and redshifted galaxy templates. A mixture of synthetic point-like andextended sources are simulated in order to estimate completeness. Derived number counts have been compared to the results ofsimilar surveys. Lyman break galaxy candidates were selected using color criteria: UBR, BRI, BVI and VRI, and their numbers computed and compared to other surveys.We have obtained photometric redshifts by spectral energy distribution template fitting. The photometric redshifts were calibrated using a sample of galaxies in the HDF-S with available spectroscopic redshifts that have also been observed with the same filter set as used here.

Results. Using a seeing weighted method to combine the science frames resulted in an increase of the number of faint objects detectedand minimizing the photometric errors. The astrometric accuracy is 0.400 arcsec with respect to 2MASS and 5 sigma limiting magnitudes for UBVRI are 28.2, 29.3, 28.3, 28.5 and 27.2 respectively (Vega). The computed galaxy number counts are in good agreement with previous works, with the U band counts of this survey being one of the deepest ever obtained. The raw number counts from broadband color selected Lyman break galaxies show a good agreement for the U and B dropouts with other surveys. Photometric redshifts have a scatter of dz=0.085 with a 9.1% fraction of outliers.

Conclusions. We derive deep number counts which are found to be consistent with previous works, reproducing the bright and faintends. Especially, the stacked deep U and I band data are found to present a comptetetive combination of depth and area, comparableto HDF observations. As well as V band, comparable to Subaru and the Lockman hole observations. Our U and B dropouts are within the expected redshift range, with mean values of 3 and 3.8 respectively.

Keyword
imaging surveys, techniques: image processing, galaxies: photometry, photometric redshifts, lyman break galaxies
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-56789 (URN)
Available from: 2011-04-27 Created: 2011-04-27 Last updated: 2011-09-15Bibliographically approved
4. The Rate of Supernovae at Redshift 0.1 − 1.0: the Stockholm VIMOS Supernova Survey IV
Open this publication in new window or tab >>The Rate of Supernovae at Redshift 0.1 − 1.0: the Stockholm VIMOS Supernova Survey IV
Show others...
2012 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 545, no A96Article in journal (Other academic) Published
Abstract [en]

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.

Keyword
supernovae, supernova rates
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-56793 (URN)10.1051/0004-6361/201219364 (DOI)000309254900096 ()
Note

Author count:10;

Available from: 2011-04-27 Created: 2011-04-27 Last updated: 2012-12-17Bibliographically approved

Open Access in DiVA

fulltext(2047 kB)508 downloads
File information
File name FULLTEXT01.pdfFile size 2047 kBChecksum SHA-512
34f80a1fabe418ff41b3b1a995e1ba31070ba7b2f5fb146206190b13391534e09f077eeec4e462e93a931d6a51d83f5fc946034403a6fdc7d54179550b0209c1
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Melinder, Jens
By organisation
Department of Astronomy
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar
Total: 508 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 207 hits
ReferencesLink to record
Permanent link

Direct link