Cosmic Shear And Power Spectrum Normalization With The Hubble Space Telescope

Weak lensing by massive-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 therapy of systematic effects were discussed in an earlier paper. Our results are in step with earlier cosmic shear measurements from the ground and Wood Ranger Power Shears official site from space. We compare our cosmic shear results and Wood Ranger Power Shears shop people from other groups to the normalization from cluster abundance and galaxy surveys. We find that the mix of four latest cosmic shear measurements are considerably inconsistent with the recent normalization using these strategies, Wood Ranger Tools and buy Wood Ranger Power Shears focus on doable explanations for the discrepancy. Weak gravitational lensing by massive-scale structure has been shown to be a precious method of measuring mass fluctuations within the universe (see Mellier at al. This impact has been detected each 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 shop from area (Rhodes, Refregier, & Groth 2001, RRGII; Hämmerle et al. 2001). These results bode properly for the prospect of measuring cosmological parameters and Wood Ranger Power Shears shop the mass distribution of the universe utilizing weak lensing. On this letter, we current the highest significance detection of cosmic shear utilizing house-based mostly photographs. It is based on photos 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 Wood Ranger Power Shears shop detection of shear we have now beforehand Wood Ranger Power Shears shop developed (Rhodes, buy Wood Ranger Power Shears Refregier, and Wood Ranger Power Shears reviews Groth 2000; RRGI) to 271 WFPC2 fields within 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 in comparison with floor-based mostly measurements. We develop an optimum depth-weighted average of chosen MDS fields to extract a weak lensing signal.



We then use this sign to derive constraints on the amplitude of the mass Wood Ranger Power Shears shop spectrum and examine 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 selected solely the I-band photos in chips 2,3, and 4 to study weak lensing. To make sure random strains-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 find out the position, magnitude, and area of every object, as well as to separate galaxies from stars. We used the chip-specific backgrounds listed within the MDS skysig recordsdata, that are in step with backgrounds calculated using the IRAF activity imarith. Not using object-particular 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 pictures is described intimately in RRGI (1999) (see additionally RRGII and Rhodes 1999). It relies on the strategy launched by Kaiser, Squires, and Broadhurst (1995), however modified and examined for functions to HST photos. The usefulness of our methodology was demonstrated by our detection of cosmic shear within the HST Groth Strip (RRGII). We correct for digital camera distortion and convolution by the anisotropic PSF using gaussian-weighted moments. Camera distortions were corrected using a map derived from stellar astrometric shifts (Holtzman, et al., 1995). PSF corrections were determined from HST observations of four stellar fields These fields have been chosen to span the main focus range of the HST as shown by Biretta et al. G𝐺G is the shear susceptibility issue given by equation (30) in RRGI. To restrict the impression of noise and systematics, we made a lot of cuts to pick out our galaxy sample.