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Published September 2007 | Published
Journal Article Open

COSMOS: Three-dimensional Weak Lensing and the Growth of Structure


We present a three-dimensional cosmic shear analysis of the Hubble Space Telescope COSMOS survey, the largest ever optical imaging program performed in space. We have measured the shapes of galaxies for the telltale distortions caused by weak gravitational lensing and traced the growth of that signal as a function of redshift. Using both 2D and 3D analyses, we measure cosmological parameters Ω_m, the density of matter in the universe, and σ_8, the normalization of the matter power spectrum. The introduction of redshift information tightens the constraints by a factor of 3 and also reduces the relative sampling (or "cosmic") variance compared to recent surveys that may be larger but are only two-dimensional. From the 3D analysis, we find that σ_8(Ω_m/0.3)^(0.44) = 0.866^(+0.085)_(-0.068) at 68% confidence limits, including both statistical and potential systematic sources of error in the total budget. Indeed, the absolute calibration of shear measurement methods is now the dominant source of uncertainty. Assuming instead a baseline cosmology to fix the geometry of the universe, we have measured the growth of structure on both linear and nonlinear physical scales. Our results thus demonstrate a proof of concept for tomographic analysis techniques that have been proposed for future weak-lensing surveys by a dedicated wide-field telescope in space.

Additional Information

© 2007 The American Astronomical Society. Received 2006 September 22; accepted 2007 January 24. The HST COSMOS Treasury program was supported through NASA grant HST-GO-09822. The HST ACS CTE calibration program is supported through NASA grant HST-AR-10964. A. L., A. R., E. S., J. P. K., L. T., and Y. M. were partly funded by the CNRS Programme National de Cosmologie. C. H. is supported by a CITA national fellowship. We thank Alan Heavens, Tom Kitching, John Peacock, Andy Taylor, and Peter Schneider for illuminating discussions. We thank Tony Roman, Denise Taylor, and David Soderblom for their assistance in planning and scheduling the extensive COSMOS observations. We thank the NASA IPAC/ IRSA staff (Anastasia Laity, Anastasia Alexov, Bruce Berriman, and John Good) for providing online archive and server capabilities for the COSMOS data sets. It is also our pleasure to gratefully acknowledge the contributions of the entire COSMOS collaboration, consisting of more than 70 scientists. More information on the COSMOS survey is available at http://www.astro .caltech.edu /~cosmos. Facilities:HST(ACS), Subaru (Suprime-Cam),CFHT(Megacam).

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