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
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.
- 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.
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:
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)
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
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).
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).
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
ApJ 577, 604 (2002):
"Weak lensing study of galaxy biasing"
H. Hoekstra, L. van Waerbeke, M. D. Gladders, Y. Mellier,
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.
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