Weak gravitational lensing has come of age as a technique for mapping large scale structure. The availability of mosaic CCD cameras on ground-based telescope and well-sampled imaging instruments on Hubble Space Telescope offers immediate prospects for tracing the distribution of dark matter on various scales. Early progress in tracing mass distributions in the peripheries of rich clusters has led to new programs aimed at tracking dark matter in filamentary structures between clusters as well as in characterising the statistical mean 'cosmic' shear on various angular scales, and measure statistically the mass associated with galaxies. Improved numerical techniques and simulations have been developed to reliably extract weak signals from faint data taking account of the various instrumental and other systematic effects which often dominate the observed signals.

Many workers have come to the conclusion that ambitious, dedicated, imaging facilities may be needed to make substantial headway in this field. Foremost, the signals are weak and it is hard to get the necessary time to conduct suitable surveys on common-user ground-based telescopes. Moreover, the fields of view of space-borne imaging cameras are inadequate (and may remain so for many years).

In making the case for new facilities, it is important to recognise that lensing is frequently viewed sceptically by the general community. The signals are weak and the burden of proof for a given result is high. Much of the lensing literature based on cluster results is apparently perceived as portraying lensing as an "interesting phenomenon" that merely reproduces results already obtained by other means. Lensing has not yet, it seems, penetrated many quarters as the unique tool we believe it to be.

The above situation is analogous to that in which microwave background workers found themselves 10-15 years ago. After much coordinated effort and theoretical support, CMB experiments now receive generous funding with both ground- and space-based experiments occurring simultaneously. There is no reason why lensing should not aspire to a similar place in experimental astronomy given the unique opportunities available.

In this context, invited participants will discuss the long term prospects for detailed studies of weak lensing. There are two basic goals. Foremost, we will discuss how to better improve the credibility and our excitement for weak lensing in the national and international communities. Secondly, we will discuss the opportunities now being explored by various groups for dedicated survey instruments. We hope here to identify the complementary nature of the various approaches.

Key topics for discussion will include:

The impact of gravitational lensing in large scale structure and cosmology and dark matter mapping:

• What are the key results we can all support with conviction?
• What can be done to validate or strengthen other results?
• How do weak lensing observations complement and when do they supercede traditional approaches?

• Appropriate analytic tools and simulations
• Wide field surveys with existing instruments
• Dedicated survey telescopes (VST, VISTA, DMT)
• Proposed arrays of modest aperture telescopes (e.g., WFHRI)
• Proposed wide field space telescopes (e.g., SNAPSAT)
• Coordination with panoramic redshift surveys (2dF, SDSS, VIRMOS, DEEP)

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Last update: 03/30/00 by: gks@astro.caltech.edu