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

We present a three dimensional cosmic shear analysis of the Hubble SpaceTelescope COSMOS survey, the largest ever optical imaging program performed inspace. We have measured the shapes of galaxies for the tell-tale distortionscaused by weak gravitational lensing, and traced the growth of that signal as afunction of redshift. Using both 2D and 3D analyses, we measure cosmologicalparameters Omega_m, the density of matter in the universe, and sigma_8, thenormalization of the matter power spectrum. The introduction of redshiftinformation tightens the constraints by a factor of three, and also reduces therelative sampling (or "cosmic") variance compared to recent surveys that may belarger but are only two dimensional. From the 3D analysis, we findsigma_8*(Omega_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 thetotal budget. Indeed, the absolute calibration of shear measurement methods isnow the dominant source of uncertainty. Assuming instead a baseline cosmologyto fix the geometry of the universe, we have measured the growth of structureon both linear and non-linear physical scales. Our results thus demonstrate aproof of concept for tomographic analysis techniques that have been proposedfor future weak lensing surveys by a dedicated wide-field telescope in space.Comment: 21 pages, 15 figures. Accepted for the COSMOS ApJ Suppl. special issu