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Weak lensing by massive-scale structure supplies a direct measurement of matter fluctuations within the universe. We report a measurement of this ‘cosmic shear’ based on 271 WFPC2 archival pictures from the Hubble Space Telescope Medium Deep Survey (MDS). Our measurement method and therapy of systematic effects have been discussed in an earlier paper. Our outcomes are per earlier cosmic shear measurements from the ground and from area. We compare our cosmic shear outcomes and those from other groups to the normalization from cluster abundance and Wood Ranger Power Shears reviews galaxy surveys. We discover that the mix of 4 recent cosmic shear measurements are somewhat inconsistent with the current normalization utilizing these strategies, and Wood Ranger Power Shears reviews talk about potential explanations for the discrepancy. Weak gravitational lensing by large-scale structure has been proven to be a useful technique of measuring mass fluctuations in the universe (see Mellier at al. This effect has been detected both from the bottom (Wittman et al.

2000; van Waerbeke et al. 2000, 2001; Bacon et al. 2000, 2002; Kaiser et al. 2000; Hoekstra et al. 2002) and Wood Ranger Power Shears order now Wood Ranger Power Shears USA Power Shears coupon from house (Rhodes, Refregier, & Groth 2001, Wood Ranger Power Shears reviews RRGII; Hämmerle et al. 2001). These results bode effectively for Wood Ranger Power Shears reviews the prospect of measuring cosmological parameters and Wood Ranger Power Shears reviews the mass distribution of the universe utilizing weak lensing. In this letter, we present the best significance detection of cosmic shear using space-based photos. It is based on images from the Hubble Space Telescope (HST) Medium Deep Survey (MDS; Ratnatunga et al. 1999). We apply the strategies for the correction of systematic results and detection of shear we've got beforehand Wood Ranger Power Shears reviews developed (Rhodes, Refregier, Wood Ranger Power Shears USA Wood Ranger Power Shears sale Wood Ranger Power Shears specs Shears price and Groth 2000; RRGI) to 271 WFPC2 fields in 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 floor-primarily based 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 different methods. The MDS consists of major and parallel observations taken with the Wide Field Planetary Camera 2 (WFPC2) on HST. We chosen only the I-band images in chips 2,3, and four to check weak lensing. To make sure random lines-of-sight, we discarded fields which have been pointed at galaxy clusters, leaving us with 468 I-band fields. We used the MDS object catalogs (Ratnatunga et al. 1999) to determine the place, 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 recordsdata, which are in line with backgrounds calculated using the IRAF activity imarith. Not utilizing object-specific backgrounds necessitated the discarding of another 20 fields with a large sky gradient. Our final catalog thus consisted of 271 WFPC2 fields amounting to an space of about 0.36 deg2.

The process we used for measuring galaxy ellipticities and shear from the source images is described in detail in RRGI (1999) (see additionally RRGII and Rhodes 1999). It is based on the tactic launched by Kaiser, Squires, and Broadhurst (1995), however modified and examined for functions to HST pictures. The usefulness of our technique was demonstrated by our detection of cosmic shear in the HST Groth Strip (RRGII). We correct for digital camera distortion and convolution by the anisotropic PSF using gaussian-weighted moments. Camera distortions had been corrected utilizing a map derived from stellar astrometric shifts (Holtzman, et al., 1995). PSF corrections have been determined from HST observations of four stellar fields These fields were chosen to span the focus vary of the HST as proven by Biretta et al. G????G is the shear susceptibility factor given by equation (30) in RRGI. To limit the influence of noise and systematics, we made a variety of cuts to pick our galaxy pattern.