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Looking at Quasars Through Galaxies
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
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.

Place, publisher, year, edition, pages
2006. Vol. 450, no 3, 971-977 p.
URN: urn:nbn:se:su:diva-12531DOI: 10.1051/0004-6361:20054329OAI: diva2:179051
Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2009-09-07Bibliographically approved
In thesis
1. Extragalactic extinction and spectral properties of Type Ia supernovae
Open this publication in new window or tab >>Extragalactic extinction and spectral properties of Type Ia supernovae
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.
Type Ia supernovae, cosmology, spectroscopy, dust extinction, quasars, axions
National Category
Physical Sciences
Research subject
urn:nbn:se:su:diva-29521 (URN)978-91-7155-912-8 (ISBN)
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

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