Weak lensing by massive-scale construction supplies a direct measurement of matter fluctuations in the universe. We report a measurement of this ‘cosmic shear’ based mostly on 271 WFPC2 archival photos from the Hubble Space Telescope Medium Deep Survey (MDS). Our measurement technique and treatment of systematic results had been mentioned in an earlier paper. Our outcomes are consistent with earlier cosmic shear measurements from the bottom and from space. We evaluate our cosmic shear outcomes and those from different groups to the normalization from cluster abundance and galaxy surveys. We discover that the mix of 4 current cosmic shear measurements are somewhat inconsistent with the recent normalization utilizing these strategies, Wood Ranger Power Shears official site and discuss attainable explanations for the discrepancy. Weak gravitational lensing by massive-scale construction has been proven to be a priceless 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 official site 2001; Bacon et al. 2000, 2002; Kaiser et al. 2000; Hoekstra et al. 2002) and from area (Rhodes, Refregier, cordless power shears & Groth 2001, Wood Ranger shears RRGII; Hämmerle et al. 2001). These outcomes bode well for the prospect of measuring cosmological parameters and the mass distribution of the universe using weak lensing. In this letter, orchard maintenance tool we present the very best significance detection of cosmic shear using house-primarily based images. It relies on photographs from the Hubble Space Telescope (HST) Medium Deep Survey (MDS; Ratnatunga et al. 1999). We apply the methods for orchard maintenance tool the correction of systematic results and detection of shear we now have beforehand orchard maintenance tool developed (Rhodes, Refregier, Wood Ranger brand shears and orchard maintenance tool Groth 2000; RRGI) to 271 WFPC2 fields within the MDS. 0.8" from the ground). This affords us a higher floor density of resolved galaxies as well as a diminished sensitivity to PSF smearing when compared to ground-based mostly measurements. We develop an optimal depth-weighted common of selected MDS fields to extract a weak lensing signal.

We then use this sign to derive constraints on the amplitude of the mass energy spectrum and compare this to measurements from previous cosmic shear surveys and from different strategies. The MDS consists of primary and parallel observations taken with the Wide Field Planetary Camera 2 (WFPC2) on HST. We chosen solely the I-band images in chips 2,3, and 4 to study 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 determine the position, magnitude, and area of each object, in addition to to separate galaxies from stars. We used the chip-particular backgrounds listed within the MDS skysig recordsdata, which are consistent with backgrounds calculated utilizing the IRAF job imarith. Not using object-specific backgrounds necessitated the discarding of one other 20 fields with a large sky gradient. Our last catalog thus consisted of 271 WFPC2 fields amounting to an space of about 0.36 deg2.

The procedure we used for measuring galaxy ellipticities and shear from the source photographs is described intimately in RRGI (1999) (see additionally RRGII and Rhodes 1999). It is predicated on the strategy introduced by Kaiser, Squires, and Broadhurst (1995), but modified and examined for functions to HST photographs. The usefulness of our technique was demonstrated by our detection of cosmic shear in the HST Groth Strip (RRGII). We appropriate for camera 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 have been decided from HST observations of 4 stellar fields These fields had been chosen to span the main focus vary of the HST as shown by Biretta et al. G