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Index - ... - Science with the Optical Monitor - Associated Weak Lensing Survey - Sunyaev-Zel'Dovich Survey - ...
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Gravitational lensing permits to probe the total mass distribution
regardless the physical state and the nature of the (dark) matter.
Weak lensing studies have more particularly focussed on the mass
distribution of a dozen of high-redshift clusters (see Fort & Mellier
1994, Schneider 1996, Mellier 1999). By measuring the tidal field
experienced by ray bundles of the distant background galaxies, the
projected mass distribution can be recovered. The statistical properties
of the shear fiels, like the rms shear or the 2-point correlation
provide a direct determination of the projected power spectrum
of the Large-Scale structures, P(k) (see Blandford et al 1991,
Miralda-Escude 1991). The non-linear evolution of the matter density
fields induces strong non-Gaussian features on scales below 10 Mpc that
can be analysed from the shear statistics on scales below 1 degre
(Bernardeau et al 1996, Jain & Seljak 1997, Van Waerbeke et al 1999).
The wide field survey described in this proposal can thus investigate the
behavior of the dark matter in these two regimes. It can be shown that
the variance and the skewness of the projected mass density (inferred
directly form the convergence 
) provide
the slope of the projected power spectrum and
independently (Bernardeau et al 1996,
Jain & Seljak 1997). The wide field data will also permit to detect
rare events produced by massive dark halos, thus providing a unique set of
shear-selected sample of clusters of galaxies and groups. Kruse &
Schneider (1999) have estimated that 10 such halos per sq. degres will be
detected, depending on the cosmological model. The statistical results can
be directly compared to the predictions of numerical
simulations. With a total area of 8° x 8° Van Waerbeke et al
(1999) have show that the shape of p(k) can be recovered
with about 1% accuracy on scales rangin from 2' to few degres. The
cosmological parameters can also be very well recovered. For instance,
a = 0.3 and a
= 1 universes can be disentangle with
more than 6 
confidence level.