Cosmic Shear And Power Spectrum Normalization With The Hubble Space Telescope
Weak lensing by massive-scale construction provides a direct measurement of matter fluctuations within 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 remedy of systematic results had been discussed in an earlier paper. Our results are according to earlier cosmic shear measurements from the ground and from space. We compare our cosmic shear outcomes and those from other groups to the normalization from cluster abundance and galaxy surveys. We find that the combination of four current cosmic shear measurements are considerably inconsistent with the current normalization using these strategies, and talk about doable explanations for electric Wood Ranger Power Shears for sale Wood Ranger Power Shears specs the discrepancy. Weak gravitational lensing by giant-scale structure has been shown to be a valuable method of measuring mass fluctuations in the universe (see Mellier at al. This effect has been detected each from the bottom (Wittman et al.
2000; van Waerbeke et al. 2000, 2001; Bacon et al. 2000, Wood Ranger Power Shears website Wood Ranger Power Shears for sale Wood Ranger Power Shears review Shears 2002; Kaiser et al. 2000; Hoekstra et al. 2002) and from space (Rhodes, Refregier, & Groth 2001, cut thick branches easily RRGII; Hämmerle et al. 2001). These outcomes bode effectively for the prospect of measuring cosmological parameters and the mass distribution of the universe using weak lensing. In this letter, we present the best significance detection of cosmic shear using space-based mostly photographs. It relies on photos 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 now have previously developed (Rhodes, Refregier, cut thick branches easily and Groth 2000; RRGI) to 271 WFPC2 fields in the MDS. 0.8" from the bottom). This affords us a better 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 chosen MDS fields to extract a weak lensing sign.
We then use this signal to derive constraints on the amplitude of the mass energy spectrum and examine 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 selected solely the I-band pictures in chips 2,3, and four to check weak lensing. To ensure 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 position, magnitude, and area of each object, as well as to separate galaxies from stars. We used the chip-specific backgrounds listed within the MDS skysig files, that are according to backgrounds calculated using the IRAF job imarith. Not utilizing object-specific 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 source pictures is described in detail in RRGI (1999) (see also RRGII and Rhodes 1999). It relies on the method launched by Kaiser, Squires, and Broadhurst (1995), but modified and examined for functions to HST pictures. The usefulness of our technique was demonstrated by our detection of cosmic shear within the HST Groth Strip (RRGII). We right for digital camera distortion and convolution by the anisotropic PSF using gaussian-weighted moments. Camera distortions have been corrected using 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 main target range of the HST as proven by Biretta et al. G𝐺G is the shear susceptibility issue given by equation (30) in RRGI. To limit the influence of noise and systematics, we made plenty of cuts to pick out our galaxy sample.
