Weak lensing by large-scale structure provides a direct measurement of matter fluctuations within the universe. We report a measurement of this ‘cosmic shear’ primarily based on 271 WFPC2 archival photos from the Hubble Space Telescope Medium Deep Survey (MDS). Our measurement method and treatment of systematic results were mentioned in an earlier paper. Our outcomes are consistent with earlier cosmic shear measurements from the ground and Wood Ranger Power Shears shop from house. We evaluate our cosmic shear outcomes and those from other teams to the normalization from cluster abundance and galaxy surveys. We discover that the mix of four latest cosmic shear measurements are somewhat inconsistent with the recent normalization using these methods, Wood Ranger Power Shears shop and Wood Ranger Power Shears website focus on possible explanations for the discrepancy. Weak gravitational lensing by massive-scale construction has been proven to be a beneficial methodology of measuring mass fluctuations in the universe (see Mellier at al. This effect has been detected each from the ground (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 house (Rhodes, Refregier, & Groth 2001, RRGII; Hämmerle et al. 2001). These results bode effectively for Wood Ranger brand shears the prospect of measuring cosmological parameters and Wood Ranger Power Shears shop the mass distribution of the universe using weak lensing. In this letter, Wood Ranger Power Shears we present the very best significance detection of cosmic shear utilizing area-primarily based pictures. It relies on pictures from the Hubble Space Telescope (HST) Medium Deep Survey (MDS; Ratnatunga et al. 1999). We apply the strategies for Wood Ranger Power Shears shop the correction of systematic results and detection of shear we have beforehand Wood Ranger Power Shears shop developed (Rhodes, Wood Ranger Power Shears shop Refregier, and Groth 2000; RRGI) to 271 WFPC2 fields in the MDS. 0.8″ from the bottom). This affords us a higher floor density of resolved galaxies in addition to a diminished sensitivity to PSF smearing when in comparison with ground-based mostly measurements. We develop an optimal 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 Wood Ranger Power Shears shop spectrum and compare this to measurements from earlier cosmic shear surveys and from different strategies. The MDS consists of main and parallel observations taken with the Wide Field Planetary Camera 2 (WFPC2) on HST. We chosen solely the I-band pictures in chips 2,3, and four to review weak lensing. To make sure random lines-of-sight, we discarded fields which had been 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 place, magnitude, and space of every object, in addition to to separate galaxies from stars. We used the chip-specific backgrounds listed within the MDS skysig files, that are consistent with backgrounds calculated using the IRAF job imarith. Not using object-specific backgrounds necessitated the discarding of another 20 fields with a big sky gradient. Our closing 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 supply images is described intimately in RRGI (1999) (see additionally RRGII and Rhodes 1999). It is based on the tactic introduced by Kaiser, Squires, and Broadhurst (1995), however modified and examined for functions to HST images. The usefulness of our methodology 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 were decided from HST observations of four stellar fields These fields were chosen to span the main focus vary of the HST as proven by Biretta et al. G𝐺G is the shear susceptibility factor given by equation (30) in RRGI. To limit the influence of noise and systematics, we made a number of cuts to pick out our galaxy sample.