Cosmic Shear and Power Spectrum Normalization with The Hubble Space Telescope > 자유게시판

Weak lensing by giant-scale construction provides a direct measurement of matter fluctuations in the universe. We report a measurement of this ‘cosmic shear’ based mostly on 271 WFPC2 archival images from the Hubble Space Telescope Medium Deep Survey (MDS). Our measurement methodology and therapy of systematic effects have been discussed in an earlier paper. Our results are consistent with earlier cosmic shear measurements from the bottom and Wood Ranger Power Shears reviews from house. We evaluate our cosmic shear outcomes and people from other teams to the normalization from cluster abundance and galaxy surveys. We discover that the combination of four current cosmic shear measurements are somewhat inconsistent with the recent normalization using these strategies, and focus on attainable explanations for the discrepancy. Weak gravitational lensing by large-scale construction has been proven to be a beneficial technique of measuring mass fluctuations within 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 from area (Rhodes, Refregier, Wood Ranger Power Shears official site & Groth 2001, Wood Ranger Power Shears official site RRGII; Hämmerle et al. 2001). These results bode nicely for the prospect of measuring cosmological parameters and electric Wood Ranger Power Shears review garden power shears the mass distribution of the universe using weak lensing. On this letter, we current the best significance detection of cosmic shear utilizing space-primarily based pictures. It is based on photographs 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 now have beforehand developed (Rhodes, cordless Wood Ranger Power Shears order now Wood Ranger Power Shears sale Refregier, and Groth 2000; RRGI) to 271 WFPC2 fields in the MDS. 0.8" from the ground). This affords us the next floor density of resolved galaxies as well as a diminished sensitivity to PSF smearing when compared to ground-based 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 Wood Ranger Power Shears official site spectrum and examine 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 selected only the I-band images in chips 2,3, and 4 to study 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 space of each object, in addition to to separate galaxies from stars. We used the chip-specific backgrounds listed within the MDS skysig files, which are in step with backgrounds calculated using the IRAF task imarith. Not utilizing object-particular backgrounds necessitated the discarding of one other 20 fields with a big sky gradient. Our last 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 supply pictures is described intimately in RRGI (1999) (see also RRGII and Rhodes 1999). It relies on the method launched by Kaiser, Squires, and Broadhurst (1995), however modified and examined for applications to HST images. The usefulness of our technique was demonstrated by our detection of cosmic shear within the HST Groth Strip (RRGII). We right for camera distortion and convolution by the anisotropic PSF utilizing gaussian-weighted moments. Camera distortions have been corrected utilizing a map derived from stellar astrometric shifts (Holtzman, et al., 1995). PSF corrections had been determined from HST observations of four stellar fields These fields have been chosen to span the main focus vary of the HST as proven by Biretta et al. G