Position of the targets

The VIRMOS-DESCART Cosmic Shear Survey at CFHT

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PI: Y. Mellier
Co-I: F. Bernardeau, E. Bertin, H. J. McCracken, J.-C. Cuillandre, M. Dantel-Fort, T. Erben, B. Fort, S. Foucaud, H. Hoekstra, B. Jain, O. Le Fevre, R. Maoli, U.L. Pen, E. Semboloni, I. Tereno, L. van Waerbeke

The CFHT VIRMOS-DESCART Cosmic Shear survey focuses on weak lensing distortion analysis from one degree down to arc-minute scales. It produces similar quantities as the VLT-DESCART on only 4 uncorrelated fields (instead of 55 for the VLT) but probes distortion patterns on a field of view 20 times larger. The VIRMOS-DESCART survey
  • permits similar analyses on scales larger than the VLT project;
  • probes directly the distribution of the dark matter projected along the line of sight. From this survey we expect to recover the shape of the power spectrum from one degree down to one arcminute scales and to reconstruct the mass map of the projected mass density distribution
  • uses also other bands in order to get the photometric redshifts of the lensed galaxies. Used jointly with the correlation between the mass map and the galaxy map, it can be used to derived interesting informations on the biasing.
This program is much more challenging and time consuming than the VLT project. It requests high-level data processing, automated data analysis pipelines as well as several numerical simulation tools to control systematics and to interpret cosmic shear signal in cosmological scenarios of structure formation. One critical issue is non-gravitational distortion of galaxies: wide field CCD cameras have optical distortions and are sensitive to differential atmospheric refraction. Both produce PSF anisotropy that must be handled carefully. Further, cosmic variance demands very large areas to be covered.

The VIRMOS-Descart data set:
Additional data in U and NIR bands have been obtained for the VIRMOS imaging survey. These complementary data will be important for the Weak Lensing survey in order to get information on the distances of the lenses and the sources, using photometric redshifts techniques.

VIRMOS-Descart scientific results:
  1. A&A 358, 30 (2000): "Detection of correlated galaxy ellipticities on CFHT data: first evidence for gravitational lensing by large-scale structure" by L. Van Waerbeke (CITA), Y. Mellier (IAP, Obs Paris), T. Erben (MPA), J.C. Cuillandre (CFHT), F. Bernardeau (CEA Saclay), R. Maoli (IAP), E. Bertin (IAP, Obs Paris), H.J. Mc Cracken (LAS), O. Le Fevre (LAS), B . Fort (IAP), M. Dantel-Fort (Obs Paris), B. Jain (JHU), P. Schneider (MPA)
  2. A&A 374, 757 (2001): "Cosmic Shear Statistics and Cosmology" by L. Van Waerbeke, Y. Mellier, M. Radovich, E. Bertin, M. Dantel-Fort, H.J. McCracken, O. Le Fevre, S. Foucaud, J.-C. Cuillandre, T. Erben, B. Jain, P. Schneider, F. Bernardeau, B. Fort
  3. ApJ 567, 31 (2002): "Gravity and Non-gravity Modes in the VIRMOS-DESCART Weak Lensing Survey" by U.-L. Pen (CITA), L. Van Waerbeke (IAP), Y. Mellier (IAP).
  4. A&A 389, 28 (2002): "Detection of Non-Gaussian Signatures in the VIRMOS_DESCART Lensing Survey" by S. Bernardeau (SPhT), Y. Mellier (IAP, Obs. Paris), L. van Waerbeke (IAP).
  5. A&A 393, 369 (2002): "Likelihood Analysis of Cosmic Shear on Simulated and VIRMOS-DESCART Data" by L. van Waerbeke (IAP), Y. Mellier (IAP), P. Pello (Obs. Toulouse), U.-L. Pen (CITA), H. McCracken (Obs. Bologna and LAM Marseille), B. Jain (Univ. Penn.).
  6. ApJ 577, 604 (2002): "Weak lensing study of galaxy biasing" H. Hoekstra, L. van Waerbeke, M. D. Gladders, Y. Mellier, H.K.C. Yee.
  7. ApJ 592, 664 (2003): "Detection of Dark Matter Skewness in the VIRMOS-DESCART Survey: Implications for Omega_o" U.L. Pen, T. Zhang, L. van Waerbeke, Y. Mellier, P. Zhang, J. Dubinski.
  8. MNRAS 346, 994 (2003) "The three-dimensional power spectrum of dark and luminous matter from the VIRMOS-DESCART cosmic shear survey" U.L. Pen, T. Lu, L. van Waerbeke, Y. Mellier

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Last modifications: december 21, 2003