Evidence of the accelerated expansion of the Universe from weak lensing tomography with COSMOS
Abstract
We present a comprehensive analysis of weak gravitational lensing by largescale structure in the Hubble Space Telescope Cosmic Evolution Survey (COSMOS), in which we combine spacebased galaxy shape measurements with groundbased photometric redshifts to study the redshift dependence of the lensing signal and constrain cosmological parameters. After applying our weak lensingoptimized data reduction, principalcomponent interpolation for the spatially, and temporally varying ACS pointspread function, and improved modelling of chargetransfer inefficiency, we measured a lensing signal that is consistent with pure gravitational modes and no significant shape systematics. We carefully estimated the statistical uncertainty from simulated COSMOSlike fields obtained from raytracing through the Millennium Simulation, including the full nonGaussian sampling variance. We tested our lensing pipeline on simulated spacebased data, recalibrated nonlinear power spectrum corrections using the raytracing analysis, employed photometric redshift information to reduce potential contamination by intrinsic galaxy alignments, and marginalized over systematic uncertainties. We find that the weak lensing signal scales with redshift as expected from general relativity for a concordance ΛCDM cosmology, including the full crosscorrelations between different redshift bins. Assuming a flat ΛCDM cosmology, we measure σ_8(Ω_m/0.3)^{0.51} = 0.75±0.08 from lensing, in perfect agreement with WMAP5, yielding joint constraints Ω_m = 0.266^{+0.025}_{0.023}, σ_8 = 0.802^{+0.028}_{0.029} (all 68.3% conf.). Dropping the assumption of flatness and using priors from the HST Key Project and BigBang nucleosynthesis only, we find a negative deceleration parameter q_{0} at 94.3% confidence from the tomographic lensing analysis, providing independent evidence of the accelerated expansion of the Universe. For a flat wCDM cosmology and prior w ∈ [2,0], we obtain w <0.41 (90% conf.). Our dark energy constraints are still relatively weak solely due to the limited area of COSMOS. However, they provide an important demonstration of the usefulness of tomographic weak lensing measurements from space.
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archives at the Space Telescope European Coordinating Facility and the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 526555.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 June 2010
 DOI:
 10.1051/00046361/200913577
 arXiv:
 arXiv:0911.0053
 Bibcode:
 2010A&A...516A..63S
 Keywords:

 cosmological parameters;
 dark matter;
 largescale structure of Universe;
 gravitational lensing: weak;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 26 pages, 25 figures, matches version accepted for publication by Astronomy and Astrophysics