Cosmic Shear and Power Spectrum Normalization with The Hubble Space Te…

Weak lensing by large-scale structure provides a direct measurement of matter fluctuations within the universe. We report a measurement of this ‘cosmic shear’ based on 271 WFPC2 archival photographs from the Hubble Space Telescope Medium Deep Survey (MDS). Our measurement technique and treatment of systematic results had been discussed in an earlier paper. Our results are according to earlier cosmic shear measurements from the bottom and Wood Ranger Power Shears official site from space. We evaluate our cosmic shear outcomes and people from different teams to the normalization from cluster abundance and galaxy surveys. We find that the mixture of 4 recent cosmic shear measurements are somewhat inconsistent with the recent normalization utilizing these methods, and talk about potential explanations for the discrepancy. Weak gravitational lensing by large-scale structure has been proven to be a helpful technique of measuring mass fluctuations within the universe (see Mellier at al. This effect has been detected each from the bottom (Wittman et al.

2000; van Waerbeke et al. 2000, Wood Ranger Power Shears reviews 2001; Bacon et al. 2000, Wood Ranger Power Shears reviews 2002; Kaiser et al. 2000; Hoekstra et al. 2002) and from house (Rhodes, Wood Ranger Power Shears reviews Refregier, & Groth 2001, Wood Ranger Power Shears reviews RRGII; Hämmerle et al. 2001). These results bode effectively for the prospect of measuring cosmological parameters and the mass distribution of the universe using weak lensing. In this letter, Wood Ranger Power Shears reviews we present the highest significance detection of cosmic shear using area-based mostly pictures. It is based on photos from the Hubble Space Telescope (HST) Medium Deep Survey (MDS; Ratnatunga et al. 1999). We apply the strategies for Wood Ranger Power Shears website the correction of systematic effects and Wood Ranger Power Shears website detection of shear we have previously developed (Rhodes, Wood Ranger Power Shears Refregier, Wood Ranger Power Shears reviews and Wood Ranger Power Shears reviews Groth 2000; RRGI) to 271 WFPC2 fields within the MDS. 0.8" from the ground). This affords us the next surface density of resolved galaxies in addition to a diminished sensitivity to PSF smearing when compared to ground-based mostly measurements. We develop an optimum depth-weighted common of chosen MDS fields to extract a weak lensing signal.

We then use this signal to derive constraints on the amplitude of the mass energy spectrum and compare this to measurements from earlier cosmic shear surveys and from other methods. The MDS consists of primary and parallel observations taken with the Wide Field Planetary Camera 2 (WFPC2) on HST. We selected solely the I-band photos in chips 2,3, and 4 to check weak lensing. To make sure random strains-of-sight, we discarded fields which were pointed at galaxy clusters, leaving us with 468 I-band fields. We used the MDS object catalogs (Ratnatunga et al. 1999) to find out the position, magnitude, and space of each object, in addition to to separate galaxies from stars. We used the chip-particular backgrounds listed in the MDS skysig information, which are consistent with backgrounds calculated utilizing the IRAF activity imarith. Not utilizing object-specific backgrounds necessitated the discarding of another 20 fields with a large sky gradient. Our last catalog thus consisted of 271 WFPC2 fields amounting to an area of about 0.36 deg2.

The process we used for measuring galaxy ellipticities and shear from the source photographs is described in detail in RRGI (1999) (see also RRGII and Rhodes 1999). It is predicated on the strategy introduced by Kaiser, Squires, and Broadhurst (1995), however modified and tested for purposes to HST photos. The usefulness of our technique was demonstrated by our detection of cosmic shear within the HST Groth Strip (RRGII). We appropriate for digicam distortion and convolution by the anisotropic PSF utilizing gaussian-weighted moments. Camera distortions were corrected using a map derived from stellar astrometric shifts (Holtzman, et al., 1995). PSF corrections had been decided from HST observations of four stellar fields These fields have been chosen to span the focus vary of the HST as shown by Biretta et al. G