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On quasar host galaxies as tests of non-cosmological redshifts
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
2005 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 359, no 3, 1193-1200 p.Article in journal (Refereed) Published
Abstract [en]

Despite a general consensus in the astronomical community that all quasars are located at the distances implied by their redshifts, a number of observations still challenge this interpretation, possibly indicating that some subpopulation of quasars may harbour significant redshift components not related to the expansion of the Universe. It has been suggested that these objects may have been ejected from local galaxies and are likely to evolve into new galaxies themselves. Here, a test of such exotic scenarios is proposed, based on the spectral energy distribution of the galaxies hosting quasars with suspected ejection origin. Provided that the time-scales over which the ejected objects manifest themselves as quasars is short, one would in the framework of the ejection scenarios expect to find either no quasar host galaxy, a pseudo-host consisting of gas ionized by the quasar, or a host galaxy consisting of young stars only. It is argued that the spectral energy distributions corresponding to the last two options should differ significantly from that of most quasar host galaxies detected at low redshift so far, thus providing a potential test of the claimed existence of ejected quasars. A minimal implementation of this test, involving optical and near-infrared broad-band photometry, is suggested.

Place, publisher, year, edition, pages
2005. Vol. 359, no 3, 1193-1200 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-93163DOI: 10.1111/j.1365-2966.2005.08989.xOAI: oai:DiVA.org:uu-93163DiVA: diva2:166554
Available from: 2005-05-09 Created: 2005-05-09 Last updated: 2013-05-22Bibliographically approved
In thesis
1. Quasars and Low Surface Brightness Galaxies as Probes of Dark Matter
Open this publication in new window or tab >>Quasars and Low Surface Brightness Galaxies as Probes of Dark Matter
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Kvasarer och ytljussvaga galaxer som redskap för att studera den mörka materian
Abstract [en]

Most of the matter in the Universe appears to be in some form which does not emit or absorb light. While evidence for the existence of this dark matter has accumulated over the last seventy years, its nature remains elusive. In this thesis, quasars and low surface brightness galaxies (LSBGs) are used to investigate the properties of the dark matter.

Quasars are extremely bright light sources which can be seen over vast distances. These cosmic beacons may be used to constrain dark matter in the form of low-mass, compact objects along the line of sight, as such objects are expected to induce brightness fluctuations in quasars through gravitational microlensing effects. Using a numerical microlensing model, we demonstrate that the uncertainty in the typical size of the optical continuum-emitting region in quasars represents the main obstacle in this procedure. We also show that, contrary to claims in the literature, microlensing fails to explain the observed long-term optical variability of quasars. Here, quasar distances are inferred from their redshifts, which are assumed to stem from the expansion of the Universe. Some astronomers do however defend the view that quasar redshifts could have a different origin. A number of potential methods for falsifying claims of such non-cosmological redshifts are proposed.

As the ratio of dark to luminous matter is known to be unusually high in LSBGs, these objects have become the prime targets for probing dark matter halos around galaxies. Here, we use spectral evolutionary models to constrain the properties of the stellar populations in a class of unusually blue LSBGs. Using rotation curve data obtained at the ESO Very Large Telescope, we also investigate the density profiles of their dark halos. We find our measurements to be inconsistent with the predictions of the currently favoured cold dark matter scenario.

Place, publisher, year, edition, pages
Uppsala: Institutionen för astronomi och rymdfysik, 2005. viii + 87 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 60
Astronomy, Cosmology: dark matter, gravitational lensing, quasars: general, quasars: redshift, galaxies: halos, galaxies: formation, galaxies: stellar content, Astronomi
National Category
Astronomy, Astrophysics and Cosmology
urn:nbn:se:uu:diva-5826 (URN)91-554-6273-1 (ISBN)
Public defence
2005-06-02, Polhemssalen, Ångström Laboratory, Uppsala, 10:15
Available from: 2005-05-09 Created: 2005-05-09Bibliographically approved

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