Dihydralazin

Schneider, Achim; Schlunck, Günther; Sieber, Viola

doi:10.1007/978-3-642-97317-8_55

Cited by 18 publications

(26 citation statements)

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“…This relation holds for a wide class of smooth analytic lens models (i.e. Schneider & Weiss 1992;Keeton, Gaudi & Petters 2003); on the other hand, all known observed lensed QSOs violate this relation which has been explained as due to the presence of the CDM substructure within the lensing galaxy's halo. However, some of these discrepant systems may be due to microlensed stars rather than due to the CDM substructure .…”

Section: Introductionmentioning

confidence: 93%

“…In this paper, we will mainly concentrate on the cusp configuration that corresponds to a source located close to the cusp of the inner caustic curve. The behaviour of the gravitational lens mapping near a cusp was first studied by Blandford & Narayan (1986), Schneider & Weiss (1992), Mao (1992) and Zakharov (1995), who investigated the magnification properties of the cusp images, and concluded that the sum of the signed magnification factors of the three merging images approaches zero as the source moves towards the cusp. In other words (e.g.…”

Section: Cusp Caustic Relationmentioning

confidence: 99%

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Radial distribution and strong lensing statistics of satellite galaxies and substructure using high-resolution CDM hydrodynamical simulations

Macciò

Moore

Stadel

et al. 2006

Monthly Notices of the Royal Astronomical Society

110

133

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We analyse the number density and radial distribution of substructures and satellite galaxies using cosmological simulations that follow the gas dynamics of a baryonic component, including shock heating, radiative cooling and star formation within the hierarchical concordance Lambda cold dark matter model. We find that the dissipation of the baryons greatly enhances the survival of subhaloes, especially in the galaxy core, resulting in a radial distribution of satellite galaxies that closely follows the overall mass distribution. Hydrodynamical simulations are necessary to resolve the adiabatic contraction and dense cores of galaxies, resulting in a total number of satellites a factor of 2 larger than that found in pure dark matter simulation, in good agreement with the observed spatial distribution of satellite galaxies within galaxies and clusters. Convergence tests show that the cored distribution found by previous authors in pure N‐body simulations was due to the physical overmerging of dark matter only structures. We proceed to use a ray‐shooting technique in order to study the impact of these additional substructures on the number of violations of the cusp caustic magnification relation. We develop a new approach to try to disentangle the effect of substructures from the intrinsic discreteness of N‐body simulations. Even with the increased number of substructures in the centres of galaxies, we are not able to reproduce the observed high numbers of discrepancies observed in the flux ratios of multiply lensed quasars.

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Section: Introductionmentioning

confidence: 93%

Section: Cusp Caustic Relationmentioning

confidence: 99%

Radial distribution and strong lensing statistics of satellite galaxies and substructure using high-resolution CDM hydrodynamical simulations

Macciò

Moore

Stadel

et al. 2006

Monthly Notices of the Royal Astronomical Society

110

133

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“…This process is repeated for all the grid points. The cusp-caustic relation states that as the three images move close together, the quantity R cusp should tend to zero (Blandford & Narayan 1986;Schneider & Weiss 1992;Zakharov 1995;Keeton et al 2003). Fig.…”

Section: The Cusp-caustic Relationmentioning

confidence: 99%

Simulations of strong gravitational lensing with substructure

Amara¹,

Metcalf²,

Cox³

et al. 2006

Monthly Notices of the Royal Astronomical Society

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Galactic‐sized gravitational lenses are simulated by combining a cosmological N‐body simulation and models for the baryonic component of the galaxy. The lens caustics, critical curves, image locations and magnification ratios are calculated by ray shooting on an adaptive grid. When the source is near a cusp in a smooth lens' caustic, the sum of the magnifications of the three closest images should be close to zero. It is found that in the observed cases this sum is generally too large to be consistent with the simulations, implying that there is not enough substructure in the simulations. This suggests that other factors play an important role. These may include limited numerical resolution, lensing by structure outside the halo, selection bias and the possibility that a randomly selected galaxy halo may be more irregular, for example, due to recent mergers, than the isolated halo used in this study. It is also shown that, with the level of substructure computed from the N‐body simulations, the image magnifications of the Einstein cross‐type lenses are very weak functions of source size up to 1 kpc. This is also true for the magnification ratios of widely separated images in the fold and cusp–caustic lenses. This means that selected magnification ratios for the different emission regions of a lensed quasar should agree with each other, barring microlensing by stars. The source size dependence of the magnification ratio between the closest pair of images is more sensitive to substructure.

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“…For a cusp lens, we expect the three brightest images to satisfy the magnification sum rule (e.g. Schneider & Weiss 1992;Mao & Schneider 1998;Keeton, Gaudi & Petters 2003) µ 1 + µ 2 + µ 3 ≈ 0.…”

Section: Introductionmentioning

confidence: 99%

Multipole models of four-image gravitational lenses with anomalous flux ratios

Congdon¹,

Keeton²

2005

Monthly Notices of the Royal Astronomical Society

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It has been known for over a decade that many four‐image gravitational lenses exhibit anomalous radio flux ratios. These anomalies can be explained by adding a clumpy cold dark matter (CDM) component to the background galactic potential of the lens. As an alternative, Evans & Witt (2003) recently suggested that smooth multipole perturbations provide a reasonable alternative to CDM substructure in some but not all cases. We generalize their method in two ways so as to determine whether multipole models can explain highly anomalous systems. We carry the multipole expansion to higher order, and also include external tidal shear as a free parameter. Fitting for the shear proves crucial to finding a physical (positive‐definite density) model. For B1422+231, working to order kmax= 5 (and including shear) yields a model that is physical but implausible. Going to higher order (kmax≳ 9) reduces global departures from ellipticity, but at the cost of introducing small‐scale wiggles in proximity to the bright images. These localized undulations are more pronounced in B2045+265, where kmax∼ 17 multipoles are required to smooth out large‐scale deviations from elliptical symmetry. Such modes surely cannot be taken at face value; they must indicate that the models are trying to reproduce some other sort of structure. Our formalism naturally finds models that fit the data exactly, but we use B0712+472 to show that measurement uncertainties have little effect on our results. Finally, we consider the system B1933+503, where two sources are lensed by the same foreground galaxy. The additional constraints provided by the images of the second source render the multipole model unphysical. We conclude that external shear must be taken into account to obtain plausible models, and that a purely smooth angular structure for the lens galaxy does not provide a viable alternative to the prevailing CDM clump hypothesis.

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Dihydralazin

Cited by 18 publications

References 0 publications

Radial distribution and strong lensing statistics of satellite galaxies and substructure using high-resolution CDM hydrodynamical simulations

Radial distribution and strong lensing statistics of satellite galaxies and substructure using high-resolution CDM hydrodynamical simulations

Simulations of strong gravitational lensing with substructure

Multipole models of four-image gravitational lenses with anomalous flux ratios

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