Cosmic Shear And Power Spectrum Normalization With The Hubble Space Telescope
Weak lensing by giant-scale construction supplies a direct measurement of matter fluctuations in the universe. We report a measurement of this ‘cosmic shear’ based on 271 WFPC2 archival photographs from the Hubble Space Telescope Medium Deep Survey (MDS). Our measurement technique and treatment of systematic results have been discussed in an earlier paper. Our results are consistent with earlier cosmic shear measurements from the ground and from area. We compare our cosmic shear outcomes and people from other teams to the normalization from cluster abundance and galaxy surveys. We discover that the mixture of 4 current cosmic shear measurements are somewhat inconsistent with the latest normalization utilizing these methods, and focus on possible explanations for the discrepancy. Weak gravitational lensing by massive-scale construction has been proven to be a invaluable method 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, fast orchard maintenance 2001; Bacon et al. 2000, 2002; Kaiser et al. 2000; Hoekstra et al. 2002) and Wood Ranger Power Shears warranty Ranger Power Shears coupon from space (Rhodes, Refregier, & Groth 2001, Wood Ranger Power Shears specs Ranger Power Shears review RRGII; Hämmerle et al. 2001). These outcomes bode properly for the prospect of measuring cosmological parameters and fast orchard maintenance the mass distribution of the universe using weak lensing. In this letter, we current the best significance detection of cosmic shear utilizing space-primarily based photos. 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 effects and fast orchard maintenance detection of shear we have now beforehand developed (Rhodes, Refregier, fast orchard maintenance 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 in addition to a diminished sensitivity to PSF smearing when compared to floor-based mostly measurements. We develop an optimal depth-weighted average of selected MDS fields to extract a weak lensing signal.
We then use this sign to derive constraints on the amplitude of the mass power spectrum and examine this to measurements from previous cosmic shear surveys and from other methods. The MDS consists of major and parallel observations taken with the Wide Field Planetary Camera 2 (WFPC2) on HST. We chosen only the I-band photos in chips 2,3, and four to study weak lensing. To ensure random traces-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-particular backgrounds listed within the MDS skysig information, that are according to backgrounds calculated utilizing the IRAF process imarith. Not utilizing object-specific backgrounds necessitated the discarding of another 20 fields with a large sky gradient. Our final 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 photos is described in detail in RRGI (1999) (see also RRGII and Rhodes 1999). It is based on the strategy introduced by Kaiser, Squires, and Broadhurst (1995), however modified and tested for functions to HST photos. The usefulness of our method was demonstrated by our detection of cosmic shear in the HST Groth Strip (RRGII). We correct for digicam 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 have been determined from HST observations of 4 stellar fields These fields had been chosen to span the main focus vary of the HST as shown by Biretta et al. G𝐺G is the shear susceptibility factor given by equation (30) in RRGI. To limit the affect of noise and systematics, we made quite a lot of cuts to pick our galaxy sample.
