LSST Probes of Dark Energy with Weak Lensing: Ground versus Space

Details LSST Probes of Dark Energy with Weak Lensing: Ground versus Space LSST Probes of Dark Energy with Weak Lensing: Ground versus Space

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21540114j&link_type=abstract

American Astronomical Society, AAS Meeting #215, #401.14; Bulletin of the American Astronomical Society, Vol. 42, p.219

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Weak lensing provides a clean probe of dark matter, constraining models of dark energy by measuring the evolution of the cosmic shear. The power of a lensing survey for cosmology depends on the total number of resolved distant galaxies and the sky coverage of the survey.
Galaxy shape measurement depends on galaxy angular size, delivered PSF, and limiting surface brightness. At the same surface brightness, the number density of usable galaxies is a factor of 2-3 higher in space because of the diffraction-limited seeing. However, a carefully designed, wide-field, large-aperture ground-based telescope ( 0.7” median seeing in r band) can surpass space-based observatories in the total yield and sky coverage. The larger number of images per galaxy obtained by such a survey would greatly aid control of systematics.
For a quantitative estimate of LSST performance, we are carrying out a suite of WL simulations including atmospheric turbulence, telescope aberrations, and detector focal plane height fluctuations assuming worst-case scenarios. Our results show that the residual PSF correlation function for the LSST main survey is below statistical errors for angular scales of interest for cosmology. These results are valid for a galaxy number density 40 per sq. arcmin. Although a space-based survey could reduce the error of the shear power spectrum relative to the LSST at small scales (l > 104), where the baryonic effect complicates interpretation, the LSST outperforms a space survey at large scales, where the errors are dominated by sample variance, and the primary cosmological information lies.

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