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

Weak lensing by large-scale construction offers a direct measurement of matter fluctuations within the universe. We report a measurement of this ‘cosmic shear’ based mostly on 271 WFPC2 archival pictures from the Hubble Space Telescope Medium Deep Survey (MDS). Our measurement technique and therapy of systematic effects had been discussed in an earlier paper. Our outcomes are per earlier cosmic shear measurements from the bottom and from area. We compare our cosmic shear results and those from other teams to the normalization from cluster abundance and gardening shears galaxy surveys. We find that the mix of 4 latest cosmic shear measurements are somewhat inconsistent with the current normalization using these strategies, and talk about attainable explanations for the discrepancy. Weak gravitational lensing by large-scale structure has been shown to be a valuable methodology of measuring mass fluctuations within the universe (see Mellier at al. This impact has been detected both from the ground (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 warranty from space (Rhodes, Refregier, & Groth 2001, RRGII; Hämmerle et al. 2001). These outcomes bode nicely for the prospect of measuring cosmological parameters and the mass distribution of the universe utilizing weak lensing. On this letter, we present the highest significance detection of cosmic shear utilizing house-based mostly photos. It relies on pictures from the Hubble Space Telescope (HST) Medium Deep Survey (MDS; Ratnatunga et al. 1999). We apply the methods for the correction of systematic results and detection of shear we've got previously developed (Rhodes, Refregier, Wood Ranger Power Shears shop Wood Ranger Power Shears features electric power shears Wood Ranger Power Shears order now features and Groth 2000; RRGI) to 271 WFPC2 fields in the MDS. 0.8" from the ground). This affords us a higher surface density of resolved galaxies as well as a diminished sensitivity to PSF smearing when in comparison with floor-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 Wood Ranger Power Shears warranty spectrum and evaluate this to measurements from earlier cosmic shear surveys and from other methods. The MDS consists of main and parallel observations taken with the Wide Field Planetary Camera 2 (WFPC2) on HST. We selected solely the I-band pictures in chips 2,3, and 4 to check 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 determine the place, magnitude, and area of every object, as well as to separate galaxies from stars. We used the chip-particular backgrounds listed in the MDS skysig files, which are according to backgrounds calculated utilizing the IRAF activity imarith. Not using object-particular backgrounds necessitated the discarding of one other 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 in detail in RRGI (1999) (see additionally RRGII and Rhodes 1999). It is predicated on the tactic introduced by Kaiser, Squires, and Broadhurst (1995), however modified and examined for purposes to HST images. The usefulness of our technique was demonstrated by our detection of cosmic shear in the HST Groth Strip (RRGII). We right for camera distortion and convolution by the anisotropic PSF utilizing gaussian-weighted moments. Camera distortions had been corrected utilizing a map derived from stellar astrometric shifts (Holtzman, et al., 1995). PSF corrections had been decided from HST observations of 4 stellar fields These fields have been chosen to span the focus range of the HST as shown by Biretta et al. G