: Dark matter from Ellipticity Sources CARTography

Gravitational distortion maps over very large fields permit to explore the large-scale distribution of the (dark) matter in the universe without regard on the light (galaxy and gas) distribution. By using this technique, it is possible to study the cosmic mass fluctuations.
The gravitational shear produced by the cumulative effect of the matter along the line of sights can be recovered from the gravitational distortion which increases the ellipticity of the galaxies. From these distortion patterns we can in principle
  • construct mass maps of the projected dark matter distribution,
  • recover the power spectrum of the mass density fluctuations,
  • put constrains on the cosmological parameters Omega and Lambda,
  • infer the evolution of the biasing factor with redshift and with angular scale,
provided we are able to minimize the noises and systematics produced by
  • the intrinsic ellipticity distribution of the galaxies,
  • the PSF anisotropy produced by the atmosphere and the instruments,
  • the cosmic variance.

A set of slides (general and talks) is available on our new DESCART web site in construction.

The project is aiming at mapping gravitational distortions in a field of about 100 deg^2. This is one of the main scientific goals of the MegaPrime project, that includes a refurbishing of the prime-focus of CFHT and the building of a wide field CCD camera MEGACAM under the responsablity of DAPNIA/SAp (CEA Saclay). The image processing will be done at the TERAPIX center, located at IAP.
Beyond the intrinsic scientific interest of projected mass mappings (which is discussed here) this project is part of a global search, with all possible observational means, of the large-scale structures of the Universe. Particularly interesting complementary tools will be available in the coming years, namely the VIRMOS instrument on the VLT and the XMM satellite for X-ray mapping of the deepest potential wells.
The project develops tools in order to produce robust results:
  • a pipeline for processing images from WFI, UH8K, CFH12K and MEGACAM (TERAPIX),
  • a pipeline for gravitational shear analysis,
  • a set of simulations of large-scale structures which includes gravitational lensing effects and realistics wide fields images.
  • a set of catalogs based on our surveys and that will make publicly available to the community

The new DESCART web site in construction. describes these tools and provides continuous progress reports on the project.

Last changes, 2003, December 20