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Extragalactic extinction and spectral properties of Type Ia supernovae
Stockholm University, Faculty of Science, Department of Physics. (CoPS)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of Type Ia supernovae as standardisable candles for probing cosmological parameters with high precision requires good knowledge about how the supernova light is affected along the line of sight and how the intrinsic brightness varies between objects. The work in this thesis addresses these topics.

One potential problem is if there is an evolution of the intrinsic brightness of Type Ia supernovae with redshift. To investigate this we have compared spectral features of intermediate-redshift supernovae with local ones. No redshift evolution could be detected up to z = 0.3. Correlations of the strength of some of the spectral features with supernova colour and lightcurve shape were found, in particular for the feature which primarily is a product of SiII 4130 absorption.

Another difficulty concerns dust present in the line of sight which could both dim and redden the supernovae. We investigated dust extinction in distant galaxies by comparing the colours of background quasars with what is expected for different types of dust. A wide range of fitted values of Rv, the total-to-selective extinction ratio, was found, indicating that the dust properties in other galaxies could potentially be different from the Milky Way value, Rv ~ 3.1.

The light could also be affected by an intergalactic dust population with an almost flat extinction curve. We found, using quasar observations, that any dimming larger than 0.2 magnitudes in the rest-frame B-band for a Type Ia supernova at z = 1 is ruled out. If the intergalactic dust has an extinction law similar to the one in the Milky Way, the corresponding limit would be 0.03 magnitudes.

Another problem is that if axions exist, photons could be converted to axions over large cosmological distances, in the presence of magnetic fields, leading to a dimming of distant objects. For some model parameters, a dimming as large as 0.6 magnitudes for a Type Ia supernova at z = 1 would be allowed from quasar observations.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2009. , 112 p.
Keyword [en]
Type Ia supernovae, cosmology, spectroscopy, dust extinction, quasars, axions
National Category
Physical Sciences
Research subject
URN: urn:nbn:se:su:diva-29521ISBN: 978-91-7155-912-8OAI: diva2:233981
Public defence
2009-10-02, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: In progress. Paper 5: In progress.Available from: 2009-09-10 Created: 2009-09-03 Last updated: 2011-04-27Bibliographically approved
List of papers
1. Limiting the dimming of distant type Ia supernovae
Open this publication in new window or tab >>Limiting the dimming of distant type Ia supernovae
2005 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, no 2, 5- p.Article in journal (Refereed) Published
Abstract [en]

Distant supernovae have been observed to be fainter than what is expected in a matter dominated universe. The most likely explanation is that the universe is dominated by an energy component with negative pressure, namely dark energy. However, there are several astrophysical processes that could, in principle, affect the measurements and in order to be able to take advantage of the growing supernova statistics, the control of systematic effects is crucial. We discuss two of these; extinction due to intergalactic grey dust and dimming due to photon-axion oscillations and show how their effect on supernova observations can be constrained using observed quasar colours and spectra. For a wide range of intergalactic dust models, we are able to rule out any dimming larger than 0.2 magnitudes for a type Ia supernova at z = 1. The corresponding limit for intergalactic Milky Way type dust is 0.03 magnitudes. For the more speculative model of photons mixing with axions, we find that the effect is independent of photon energy for certain combinations of parameter values and a dimming as large as 0.6 magnitudes cannot be ruled out. These effects can have profound implications for the possibility of constraining dark energy properties using supernova observations.

Type Ia supernovae, quasars, cosmology, axions, dust, intergalactic medium
National Category
Astronomy, Astrophysics and Cosmology Astronomy, Astrophysics and Cosmology
Research subject
urn:nbn:se:su:diva-29516 (URN)10.1088/1475-7516/2005/02/005 (DOI)
Available from: 2009-09-03 Created: 2009-09-03 Last updated: 2009-09-07Bibliographically approved
2. Looking at Quasars Through Galaxies
Open this publication in new window or tab >>Looking at Quasars Through Galaxies
2006 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 450, no 3, 971-977 p.Article in journal (Refereed) Published
Abstract [en]

Observations of quasars (QSOs) shining through or close to galaxies offer a way to probe the properties of the foreground matter through dust extinction and gravitational lensing. In this paper the feasibility of measuring the dust extinction properties is investigated using the backlitting of QSOs. We test our method to search for QSOs affected by intervening extinction, by matching the coordinates in the SDSS QSO DR3 catalogue with the New York University Value-Added Galaxy Catalog. In total, 164 QSO-galaxy pairs were found with a distance of less than 30 kpc between the galaxy centre and the QSO line-of-sight at the galaxy redshift. Investigating the QSO colours with multiband SDSS photometry, two pairs with galaxy redshifts z < 0.08 were found to be particularly interesting in that the QSOs show evidence of heavy Galactic type extinction with at very large optical radii in the foreground spiral galaxies. With the available data, it remains inconclusive whether the two pairs can be explained as statistical colour outliers, by host extinction or if they provide evidence of dust in the outskirts of spiral galaxies. Deeper galaxy catalogues and/or higher resolution follow-up QSO spectra would help resolve this problem. We also analyse five QSOs reported in the literature with spectroscopic absorption features originating from an intervening system. These systems are at higher redshifts than the other two and we find in most cases significantly lower best fit values of RV. The wide range of preferred values of RV found, although affected by substantial uncertainties, already indicates that the dust properties in other galaxies may be different from the Milky Way. Furthermore, the available data suggest a possible evolution in the dust properties with redshift, with lower RV at high z.

urn:nbn:se:su:diva-12531 (URN)10.1051/0004-6361:20054329 (DOI)
Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2009-09-07Bibliographically approved
3. Extinction properties of lensing galaxies
Open this publication in new window or tab >>Extinction properties of lensing galaxies
2008 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 485, no 2, 403-415 p.Article in journal (Refereed) Published
urn:nbn:se:su:diva-15098 (URN)10.1051/0004-6361:20079187 (DOI)000256890300014 ()
Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2009-09-07Bibliographically approved
4. NTT and NOT spectroscopy of SDSS-II supernovae
Open this publication in new window or tab >>NTT and NOT spectroscopy of SDSS-II supernovae
Show others...
2011 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 526, A28- p.Article in journal (Refereed) Published
Abstract [en]

Context. The Sloan Digital Sky Survey II (SDSS-II) Supernova Survey, conducted between 2005 and 2007, was designed to detect a large number of type Ia supernovae around z ~ 0.2, the redshift "gap" between low-z and high-z supernova searches. The survey has provided multi-band (ugriz) photometric lightcurves for variable targets, and supernova candidates were scheduled for spectroscopic observations, primarily to provide supernova classification and accurate redshifts. We present supernova spectra obtained in 2006 and 2007 using the New Technology Telescope (NTT) and the Nordic Optical Telescope (NOT).

Aims: We provide an atlas of supernova spectra in the range z = 0.03-0.32 that complements the well-sampled lightcurves from SDSS-II in the forthcoming three-year SDSS supernova cosmology analysis. The sample can, for example, be used for spectral studies of type Ia supernovae, which are critical for understanding potential systematic effects when supernovae are used to determine cosmological distances.

Methods: The spectra were reduced in a uniform manner, and special care was taken in estimating the uncertainties for the different processing steps. Host-galaxy light was subtracted when possible and the supernova type fitted using the SuperNova IDentification code (SNID). We also present comparisons between spectral and photometric dating using SALT lightcurve fits to the photometry from SDSS-II, as well as the global distribution of our sample in terms of the lightcurve parameters: stretch and colour.

Results: We report new spectroscopic data from 141 type Ia supernovae, mainly between -9 and +15 days from lightcurve maximum, including a few cases of multi-epoch observations. This homogeneous, host-galaxy subtracted, type Ia supernova spectroscopic sample is among the largest such data sets and unique in its redshift interval. The sample includes two potential SN 1991T-like supernovae (SN 2006on and SN 2007ni) and one potential SN 2002cx-like supernova (SN 2007ie). In addition, the new compilation includes spectra from 23 confirmed type II and 8 type Ib/c supernovae.

methods: observational, techniques: spectroscopic, supernovae: general, surveys, cosmology: observations
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics; Astronomy
urn:nbn:se:su:diva-56782 (URN)10.1051/0004-6361/201015704 (DOI)000286458400040 ()
Available from: 2011-04-27 Created: 2011-04-27 Last updated: 2012-01-25Bibliographically approved
5. Properties of Type Ia supernova spectra up to z ~0.3
Open this publication in new window or tab >>Properties of Type Ia supernova spectra up to z ~0.3
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Context: Distance estimates using Type Ia supernovae lead to the discovery of the accelerating universe a decade ago. Further high precision studies of the dynamics of the universe using supernovae are now limited by systematic uncertainties. Optical spectra of supernovae from follow-up observations of the SDSS-II Supernova Survey provide a natural testbed for investigating key uncertainties like a potential brightness evolution of the standard candle and the nature of the observed non-standard colour-brightness relation. Spectroscopic data also provides information needed to improve our understanding of the physical processes taking place in Type Ia supernova explosions.

Aims: If supernova properties change with redshift, this may be detectable through comparisons of spectral indicators. Studies of individual supernovae are needed in order to determine whether explosionproperties, and not only the population distribution, change with redshift. Similarly, a possible intrinsic colour-brightness relation can be explored through correlations with spectral properties.Methods: We describe spectral indicator studies of spectra observed at the NTT and NOT during 2006 and 2007. These benefit from excellent multi-band SDSS photometry while being at cosmological distances (z=0.05-0.3) where evolution, limiting Type Ia supernovae as standarizable candles, could be present. We perform measurements of pseudo equivalent widths and line velocities as a function of redshift and lightcurve parameters. We also present multiple Monte Carlo studies designed to determine possible systematic errors in our spectral analysis arising when comparing local high S/N supernova spectra with lower S/N host-contaminated distant spectra.Reults: We do not detect any significant signs of evolution in individual Type Ia supernova spectra up to z=0.3. Better control of selection effects (both of the local and the distant sample) is needed in orderto determine whether a population drift exists. We can confirm correlations between pseudo equivalent widths and lightcurve shape (stretch) and see indications of correlations with supernova colours. We conclude that it is possible to compare individual low S/N supernova spectra with local ones, but that care must be taken during both noise filtering and host-galaxy subtraction.  Host-galaxy contamination is the single largest source of systematic errors in our study, especially in the presence of differential slit loss.

urn:nbn:se:su:diva-29548 (URN)
Available from: 2009-09-04 Created: 2009-09-04 Last updated: 2010-01-14Bibliographically approved

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