arXiv subjects

J. -P. Kneib

Publications and source records attributed to J. -P. Kneib.

220 records · Page 13Linked to original sources

arXiv1995

Hubble Space Telescope Observations of the Lensing Cluster Abell 2218

We present a striking new Hubble Space Telescope (HST) observation of the rich cluster Abell 2218 taken with the Wide-Field and Planetary Camera (WFPC2). HST's restored image quality reveals a sizeable number of gravitationally-lensed features in this cluster, significantly more than had been identified using ground-based telescopes. The brightest arcs are resolved by HST and show internal features enabling us to identify multiply-imaged examples, confirming and improving the mass models of the cluster determined from ground-based observations. Although weak lensing has been detected statistically in this and other clusters from ground-based data, the superlative resolution of HST enables us to individually identify weakly distorted images more reliably than hitherto, with important consequences for their redshift determination. Using an improved mass model for the cluster calibrated with available spectroscopy for the brightest arcs, we demonstrate how inversion of the lensing model can be used to yield the redshift distribution of $\sim$80 faint arclets to $R\simeq25$. We present a new formalism for estimating the uncertainties in this inversion method and review prospects for interpreting our results and verifying the predicted redshifts.

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arXiv1995

The Core of Cluster-Lenses

The gravitational lensing of faint background galaxies by rich clusters is emerging as a very efficient method to constrain both the mass distribution of cluster of galaxies and probe the statistical properties of faint background galaxies. We review here the results concerning the core of cluster lenses, where recent Hubble Space Telescope (HST) images are giving a new insight in the gravitational distortion phenomena.

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arXiv1995

Detection of Weak Lensing in the Fields of Luminous Radiosources

We present a first attempt to reveal the possible existence of large foreground mass condensations directly responsible for the gravitational magnification of four distant luminous radiosources and one optical QSO. The technique uses a weak lensing analysis of the distant galaxies in the field of each source. We find a coherent shear map with a large magnification bias on the line of sight to Q1622+0328. The local shear in the field of the bright radiosources is also often correlated with nearby groups or poor clusters of galaxies. For three of them, the groups are identified as gravitational deflectors that magnify the radiosources. This suggests that a substantial amount of invisible mass is condensed in groups and poor clusters It may explain the origin of a large angular correlation between the distribution of distant radiosources and the distribution of low redshift galaxies. We discuss the feasability and consequences of a future systematic survey to investigate the problem of magnification bias in the fields of luminous distant objects and to probe the mass distributions of galaxy groups at intermediate redshifts.

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arXiv1995

Dynamics of Abell 2218 from optical and near-IR imagery of arc(let)s and ROSAT/HRI X-ray map

A mass model of the rich cluster A2218 is presented based on optical and new near-infrared images of arc(let)s and the ROSAT/HRI X-ray map. A lensing model is proposed with two dark matter clumps, centered on the two bright galaxies around which the various arcs are observed. Two of them, close to the most massive clump around the brightest galaxy, are required to be fold images, given their position angle with respect to the major axis. A third image for each of the two arcs is then predicted to be on the opposite side of the major axis. Both images are indeed found at the expected positions, with consistent magnitudes, colors and shapes. One of the arcs has a known redshift of $0.7$, and the model predicts that the other arc should be at higher redshift, $z \approx 3$. Photometric data in UBrzJK' indicates that a redshift close to 3 is indeed probable for this arc. The dark matter halo is found to be sharply peaked on the giant central galaxy. The ROSAT/HRI X-ray map shows a strongly clumped image, poorly correlated with the cD light and the mass model on scales below $\sim$ 200$h_{50}^{-1}$kpc, but similar to the distribution of galaxies and the mass model when smoothed on this scale. The large degree of central substructure implied helps to account for the discrepancy previously found (in the two massive clusters A2218 \& A1689) between the mass derived from the gravitational lenses and that derived from the X-ray profile and temperature distributions, in a model of hydrostatic equilibrium. Most of the discrepancy can probably be explained by bulk motions and acceleration of the gas, and projection effects enhancing the lensing power of the cluster.

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