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Distant supernovae and galaxies in the Stockholm VIMOS Supernova Survey
Stockholm University, Faculty of Science, Department of Astronomy.
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 [en]
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: urn:nbn:se:su:diva-62118ISBN: 978-91-7447-362-9 (print)OAI: oai:DiVA.org:su-62118DiVA: diva2:439861
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
List of papers
1. 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
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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
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: 2017-12-11Bibliographically approved
2. 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
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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: 2017-12-11Bibliographically 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
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(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. Supernova host galaxy properties at intermediate redshift - the Stockholm VIMOS Supernova Survey V
Open this publication in new window or tab >>Supernova host galaxy properties at intermediate redshift - the Stockholm VIMOS Supernova Survey V
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(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 (z0.7) supernovae (SNe), which are detected by means of monthly imaging in R and I bands with the VIMOS instrument onthe ESO VLT. The distances to the SNe are estimated using photometric redshifts facilitated by additional U, B and V imaging alsowith VIMOS.

Aims. We investigate the properties of host galaxies for two SN types, thermonuclear and core collapse, by comparing both samples.We summarize the steps necessary to produce a SN catalogue (from detection, to photometry and typing) and explain the processfollowed to identify the host galaxies and determine their properties.

Methods. Using a spectral energy distribution (SED) fitting 2 minimization code we compute spectral energy distribution, age, starformation rate (SFR), absolute magnitudes for the host galaxies of the SN sample. Such galaxies are chosen based on their photometricredshift (GOODZ) and SED (modified version of Hyperz). From comparisons of the different photometric parameters’ distributionsbetween CC and TN SN host galaxies, we derived different trends.

Results. We find that CC SNe tend to be more centrally concentrated than TN SNe, with the former being present in late-type/starforminggalaxies and the latter in all galaxy types. CC SNe seem to favor brighter galaxies than TN SNe. KS tests on the stellarmass-extinction distribution show that TN and CC are drawn from the normal galaxy population, and on the SFR-extinction indicatesthat TN SN host galaxies are culled from it as well, but CC SN host galaxies are not derived from it.

Keyword
supernova, host galaxies
National Category
Natural Sciences
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-62289 (URN)
Available from: 2011-09-13 Created: 2011-09-13 Last updated: 2011-09-15Bibliographically approved

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