Cluster Cores, Gravitational Lensing, and Cosmology

Abstract

Many multiply--imaged quasars have been found over the years, but none so far with image separation in excess of $8\arcsec$. The absence of such large splittings has been used as a test of cosmological models: the standard Cold Dark Matter model has been excluded on the basis that it predicts far too many large--separation double images. These studies assume that the lensing structure has the mass profile of a singular isothermal sphere. However, such large splittings would be produced by very massive systems such as clusters of galaxies, for which other gravitational lensing data suggest less singular mass profiles. Here we analyze two cases of mass profiles for lenses: an isothermal sphere with a finite core radius (density $\rho \propto (r^2+r_{core}^2{)}^{-1})$, and a Hernquist profile ($\rho \propto r^{-1}(r+a{)}^{-3}$). We find that small core radii $r_{core}\sim 30h^{-1}$ kpc, as suggested by the cluster data, or large $a \gsim 300 h^{-1}$ kpc, as needed for compatibility with gravitational distortion data, would reduce the number of large--angle splittings by an order of magnitude or more. Thus, it appears that these tests are sensitive both to the cosmological model (number density of lenses) and to the inner lens structure, which is unlikely to depend sensitively on the cosmology, making it difficult to test the cosmological models by large--separation quasar lensing until we reliably know the structure of the lenses themselves.

17 pages, uuencoded compressed tarred postscript file including text and 1 figure. To appear in January 20, 1996 issue of ApJ Letters

References in corpus (5)

• Observational and Theoretical Constraints on Singular Dark Matter Halos
• The Assembly of Galaxies in a Hierarchically Clustering Universe
• Substructure in Clusters and Central Galaxy Peculiar Velocities
• Detection of Lens Candidates for the Double QSO Q2345+007
• Deep Imaging of the Double Quasar 0957+561: New Constraints on H_0

Cited by in corpus (21)

• Density profiles and substructure of dark matter halos: converging results at ultra-high numerical resolution
• Compound gravitational lensing as a probe of dark matter substructure within galaxy halos
• Observations and Theoretical Implications of the Large Separation Lensed Quasar SDSS J1004+4112
• Lensing Constraints on the Cores of Massive Dark Matter Halos
• A survey for large image-separation lensed quasars
• Gravitational wave lensing as a probe of halo properties and dark matter
• Lensing of gravitational waves: efficient wave-optics methods and validation with symmetric lenses
• Gravitational Lensing Statistics in Universes Dominated by Dark Energy
• Weakly Lensed Gravitational Waves: Probing Cosmic Structures with Wave-Optics Features
• Gravitational Lens Statistics and The Density Profile of Dark Halos
• Computational Cosmology: from the Early Universe to the Large Scale Structure
• Gravitational lensing magnification without multiple imaging
• GLoW: novel methods for wave-optics phenomena in gravitational lensing
• A Survey for Large Separation Lensed FIRST Quasars
• Gas and Dark Matter Spherical Dynamics
• A Survey for Large Separation Lensed FIRST Quasars, II. Magnification Bias and Redshift Distribution
• Gravitational Lensing by Galaxy Groups in the Hubble Deep Field
• Critical Lines in Gravitational Lenses and the Determination of Cosmological Parameters
• Finding Gravitational Lenses With X-rays
• Exotic quantum statistics and thermodynamics from a number-conserving theory of Majorana fermions
• Angular separations of the lensed QSO images