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High-redshift microlensing and the spatial distribution of dark matter in the form of MACHOs
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
2007 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 475, no 2, 453-465 p.Article in journal (Refereed) Published
Abstract [en]

A substantial part of the dark matter of the Universe could be in the form of compact objects (MACHOs), detectable through gravitational microlensing effects as they pass through the line of sight to background light sources. So far, most attempts to model the effects of high-redshift microlensing by a cosmologically distributed population of MACHOs have assumed the compact objects to be randomly and uniformly distributed along the line of sight. Here, we present a more realistic model, in which the MACHOs are assumed to follow the spatial clustering of cold dark matter. Because of sightline-to-sightline variations in surface mass density, this scenario leads to substantial scatter in MACHO optical depths, which we quantify as a function of source redshift. We find that while optical depth estimates based on a uniform line-of-sight distribution are reasonable for the highest-redshift light sources, such estimates can be incorrect by a factor of 2 for the nearby (z 0.25) Universe. Hence, attempts to derive the cosmological density of MACHOs from microlensing observations of only a few independent sightlines can be subject to substantial uncertainties. We also apply this model to the prediction of microlensing-induced variability in quasars not subject to macrolensing, and demonstrate that relaxing the assumption of randomly and uniformly distributed MACHOs only has a modest impact on the predicted light curve amplitudes. This implies that the previously reported problems with microlensing as the dominant mechanism for the observed long-term optical variability of quasars cannot be solved by taking the large-scale clustering of dark matter into account

Place, publisher, year, edition, pages
2007. Vol. 475, no 2, 453-465 p.
Keyword [en]
cosmology: dark matter -- gravitational lensing -- galaxies: quasars: general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-11707DOI: 10.1051/0004-6361:20066707OAI: oai:DiVA.org:su-11707DiVA: diva2:178226
Available from: 2008-01-14 Created: 2008-01-14 Last updated: 2011-04-20Bibliographically approved
In thesis
1. Investigating the Dark Universe through Gravitational Lensing
Open this publication in new window or tab >>Investigating the Dark Universe through Gravitational Lensing
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A variety of precision observations suggest that the present universe is dominated by some unknown components, the so-called dark matter and dark energy. The distribution and properties of these components are the focus of modern cosmology and we are only beginning to understand them.

Gravitational lensing, the bending of light in the gravitational field of a massive object, is one of the predictions of the general theory of relativity. It has become an ever more important tool for investigating the dark universe, especially with recent and coming advances in observational data.

This thesis studies gravitational lensing effects on scales ranging over ten orders of magnitude to probe very different aspects of the dark universe. Implementing a matter distribution following the predictions of recent simulations, we show that microlensing by a large population of massive compact halo objects (MACHOs) is unlikely to be the source of the observed long-term variability in quasars. We study the feasibility of detecting the so far elusive galactic dark matter substructures, the so-called “missing satellites”, via millilensing in galaxies close to the line-of-sight to distant light sources. Finally, we utilise massive galaxy clusters, some of the largest structures known in the universe, as gravitational telescopes in order to detect distant supernovae, thereby gaining insight into the expansion history of the universe. We also show, how such observations can be used to put constraints on the dark matter component of these galaxy clusters.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2011. 67 p.
Keyword
cosmology, gravitational lensing, dark matter, galaxies, galaxy clusters
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-56515 (URN)978-91-7447-281-3 (ISBN)
Public defence
2011-06-01, lecture room FD5, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:15 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Submitted. Available from: 2011-05-10 Created: 2011-04-19 Last updated: 2011-05-16Bibliographically approved

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