Published in Vol. 5 of The Astronomy and Astrophysics Review, pp. 239:292 - 1994.


ARC(LET)S IN CLUSTERS OF GALAXIES

Bernard Fort and Yannick Mellier

Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique de Toulouse URA285,
14, Av. Edouard Belin, F-31400 Toulouse, France
E-mail: fort@iap.fr; mellier@iap.fr


ABSTRACT. The discovery of giant gravitational arcs and arclets in rich clusters of galaxies is one of the major events of the last decade in observational cosmology. High resolution imaging in subarcsecond seeing conditions of giant arcs gives information on the cluster potential and the matter distribution within the inner regions of clusters. Ultra-deep photometry of the clusters reveals numerous arclets with an orthoradial orientation from which one can infer the projected mass profile at large distance and the redshift distribution of the faintest distant background galaxies which are unobservable with standard spectroscopic techniques. Thanks to the strong magnification factor, the spectroscopy of giant arcs is possible and we can therefore observe with great detail a few very distant galaxies. Individual redshifts of arcs give the total mass of the lens, whereas the spectroscopy of a large sample of arcs also gives information on the redshift distribution of distant galaxies. It is obvious that cluster lenses play an important role as large natural telescopes for probing the distant universe. Finally, observations of multiple-arc configurations due to different sources may even constrain the cosmological parameters. We are now confident that gravitational lensing will be an essential tool within the next decade for observing very high redshift galaxies and the weak shear generated by the largest structures of the universe.

In this review we summarize the present status of gravitational arc(let)s surveys with particular emphasis on the most important issues which have arisen during the last years and on the prospects for the future, regarding the rebirth of the Hubble Space Telescope, the coming of a new generation of Very Large Telescopes, and the development of large CCDs in the optical and the infrared.


KEY WORDS: Gravitational Lensing - Clusters of galaxies - Cosmology


Table of Contents

ball6 INTRODUCTION

ball6 BASIC CONCEPTS OF GRAVITATIONAL LENSING
ball6 The Thin Gravitational Lens
ball6 Caustics and Formation of Arcs
ball6 The Singular Isothermal Sphere (SIS)
ball6 The Non Singular Squeezed Isothermal Potential

ball6 OBSERVATION OF ARCS
ball6 Imaging and Photometry of Arcs
ball6 Spectroscopy of Arcs

ball6 ARC(LET)S AS A PROBE OF DARK MATTER
ball6 Large Arcs and Central Potential
ball6 The Dark Matter Distribution from Giant Arcs
ball6 The Gravitationally Lensed Pairs
ball6 The Weak Distortion Regime
ball6 Microstructures in Arcs and Minilensing by Small Dark Halos
ball6 Occurrence of Arcs and Evolution of Clusters
ball6 Optical Rings
ball6 Towards Probing the Mass Spectrum of Gravitational Structures With Weak Lensing
ball6 Mapping Large Scale Structures
ball6 Weak Shear and Amplification Bias Near Radiosources

ball6 GRAVITATIONALLY LENSED IMAGES AND THE EVOLUTION OF GALAXIES
ball6 Giant Arcs
ball6 Distance of Faint Arclets

ball6 COSMOGRAPHY

ball6 FUTURE OUTLOOK

ball6 REFERENCES

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