Showing papers by "Matthias Bartelmann published in 1993"
Journal Article•
TL;DR: In this paper, the authors use the lensing properties of a model for dark matter inhomogeneities on large scales, based on the adhesion approximation, to construct artificial QSO samples.
Abstract: Large-scale correlations between Lick galaxies and radio-loud, distant QSOs have been observed and interpreted in terms of gravitational lensing (Fugmann 1990). We argue that, if gravitational lensing is indeed responsible for such correlations, this is a most remarkable observation, and try to understand whether lensing may account for it. To do so, we use the lensing properties of a model for dark matter inhomogeneities on large scales, based on the adhesion approximation, to construct artificial QSO samples. (Model) galaxy counts in the vicinity of the (synthetic) sample QSOs are then subjected to rank-order statistical analyses
9 citations
Journal Article•
TL;DR: In this article, the authors show that the collapse does not start from a comoving motion of the perturbation, but that the continuity equation requires an initial velocity perturbations directly related to the density perturbance.
Abstract: From a simple estimate for the formation time of galaxy clusters, Richstone et al. have recently concluded that the evidence for non-virialized structures in a large fraction of observed clusters points towards a high value for the cosmological density parameter Ω 0 . This conclusion was based on a study of the spherical collapse of density perturbations, assumed to follow a Gaussian probability distribution. In this paper, we extend their treatment in several respects: first, we argue that the collapse does not start from a comoving motion of the perturbation, but that the continuity equation requires an initial velocity perturbation directly related to the density perturbation
4 citations
Posted Content•
TL;DR: In this paper, a simple elliptical gravitational lens model for the quadruple lens B1422+231 was constructed and the details of the configuration cannot be easily understood in terms of this model; in particular, the flux ratios of the images are hard to reproduce.
Abstract: We construct a simple elliptical gravitational lens model for the quadruple lens B1422+231 and show that the details of the configuration cannot be easily understood in terms of this model; in particular, the flux ratios of the images are hard to reproduce. This qualitatively verifies the results from a different lens model constructed for the same object by Hogg and Blandford.
4 citations
Posted Content•
TL;DR: In this article, it was shown that clusters may be significantly more efficient for lensing than estimated from their velocity dispersion on the basis of iso- thermal-sphere models, and that the discrepancy between cluster core radii derived from lensing and from their X-ray surface brightness may be understood assuming that the intracluster gas was expelled from the cluster galaxies when the dark ''body'' of the cluster had already formed.
Abstract: {}From the lensing properties of a numerically simulated cluster, from the statistical properties of the giant arcs produced by the cluster, and from comparing the cluster properties derived both from lensing and from the X-ray properties of the intracluster gas, we conclude (1) that clusters may be significantly more efficient for lensing than estimated from their velocity dispersion on the basis of iso- thermal-sphere models, (2) that the discrepancy between cluster core radii derived from lensing and from their X-ray surface brightness may be understood assuming that the intracluster gas was expelled from the cluster galaxies when the dark `body' of the cluster had already formed, and (3) that clusters may be efficient in producing giant arcs even if they have extended cores and a fairly shallow sur- face-density profile. This may mean that arcs may be much easier to produce, and therefore more abundant, than previously estimated.
1 citations
TL;DR: Gravitational lensing is reviewed in this article, emphasising its importance as an astrophysical tool, and applications of the theory to astrophysical observations are discussed, as well as its theoretical concepts and applications.
Abstract: Gravitational lensing is reviewed emphasising its importance as an astrophysical tool. The theoretical concepts are briefly introduced and applications of the theory to astrophysical observations are discussed. From individual gravitational lens systems one can determine lens masses, estimate the sizes, the geometry, and the nature of emitting regions, and measure length scales, of which the Hubble constant is the most important. Statistical gravitational lensing is not considered.