Cosmic shear results from the deep lens survey. I. Joint constraints on Ωm and σ8 with a two-dimensional analysis

M. James Jee, J. Anthony Tyson, Michael D. Schneider, David Wittman, Samuel Schmidt, Stefan Hilbert

Research output: Contribution to journalReview articlepeer-review

110 Citations (Scopus)


We present a cosmic shear study from the Deep Lens Survey (DLS), a deep BVRz multi-band imaging survey of five 4 deg2 fields with two National Optical Astronomy Observatory (NOAO) 4 m telescopes at Kitt Peak and Cerro Tololo. For both telescopes, the change of the point-spread-function (PSF) shape across the focal plane is complicated, and the exposure-to-exposure variation of this position-dependent PSF change is significant. We overcome this challenge by modeling the PSF separately for individual exposures and CCDs with principal component analysis (PCA). We find that stacking these PSFs reproduces the final PSF pattern on the mosaic image with high fidelity, and the method successfully separates PSF-induced systematics from gravitational lensing effects. We calibrate our shears and estimate the errors, utilizing an image simulator, which generates sheared ground-based galaxy images from deep Hubble Space Telescope archival data with a realistic atmospheric turbulence model. For cosmological parameter constraints, we marginalize over shear calibration error, photometric redshift uncertainty, and the Hubble constant. We use cosmology-dependent covariances for the Markov Chain Monte Carlo analysis and find that the role of this varying covariance is critical in our parameter estimation. Our current non-tomographic analysis alone constrains the ΩM8 likelihood contour tightly, providing a joint constraint of Ω M = 0.262 ± 0.051 and σ8 = 0.868 ± 0.071. We expect that a future DLS weak-lensing tomographic study will further tighten these constraints because explicit treatment of the redshift dependence of cosmic shear more efficiently breaks the ΩM8 degeneracy. Combining the current results with the Wilkinson Microwave Anisotropy Probe 7 year (WMAP7) likelihood data, we obtain ΩM = 0.278 ± 0.018 and σ8 = 0.815 ± 0.020.

Original languageEnglish
Article number74
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2013 Mar 1

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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