KiDS-i-800: Comparing weak gravitational lensing measurements from same-sky surveys
Monthly Notices of the Royal Astronomical Society Oxford University Press 477:4 (2018) 4285-4307
Abstract:
We present a weak gravitational lensing analysis of 815 deg2of i-band imaging from the Kilo-Degree Survey (KiDS-i-800). In contrast to the deep r-band observations, which take priority during excellent seeing conditions and form the primary KiDS data set (KiDS-r-450), the complementary yet shallower KiDS-i-800 spans a wide range of observing conditions. The overlapping KiDS-i-800 and KiDS-r-450 imaging therefore provides a unique opportunity to assess the robustness of weak lensing measurements. In our analysis we introduce two new 'null' tests. The 'nulled' two-point shear correlation function uses a matched catalogue to show that the calibrated KiDS-i-800 and KiDS-r-450 shear measurements agree at the level of 1 ± 4 per cent.We use five galaxy lens samples to determine a 'nulled' galaxy-galaxy lensing signal from the full KiDS-i-800 and KiDS-r-450 surveys and find that the measurements agree to 7 ± 5 per cent when the KiDS-i-800 source redshift distribution is calibrated using either spectroscopic redshifts, or the 30-band photometric redshifts from the COSMOS survey.KiDS plus GAMA: Cosmology constraints from a joint analysis of cosmic shear, galaxy-galaxy lensing, and angular clustering
Monthly Notices of the Royal Astronomical Society Oxford University Press 476:4 (2018) 4662-4689
Abstract:
We present cosmological parameter constraints from a joint analysis of three cosmological probes: the tomographic cosmic shear signal in~450 deg2of data from the Kilo Degree Survey (KiDS), the galaxy-matter cross-correlation signal of galaxies from the Galaxies And Mass Assembly (GAMA) survey determined with KiDS weak lensing, and the angular correlation function of the same GAMA galaxies. We use fast power spectrum estimators that are based on simple integrals over the real-space correlation functions, and show that they are practically unbiased over relevant angular frequency ranges. We test our full pipeline on numerical simulations that are tailored to KiDS and retrieve the input cosmology. By fitting different combinations of power spectra, we demonstrate that the three probes are internally consistent. For all probes combined, we obtain S8≡ σ8√ Ωm/0.3 = 0.800-0.027+0.029, consistent with Planck and the fiducial KiDS-450 cosmic shear correlation function results. Marginalizing over wide priors on the mean of the tomographic redshift distributions yields consistent results for S8with an increase of 28 per cent in the error. The combination of probes results in a 26 per cent reduction in uncertainties of S8over using the cosmic shear power spectra alone. The main gain from these additional probes comes through their constraining power on nuisance parameters, such as the galaxy intrinsic alignment amplitude or potential shifts in the redshift distributions, which are up to a factor of 2 better constrained compared to using cosmic shear alone, demonstrating the value of large-scale structure probe combination.Radio weak lensing shear measurement in the visibility domain - II. Source extraction
Monthly Notices of the Royal Astronomical Society Oxford University Press 476:2 (2018) 2053-2062
Abstract:
This paper extends the method introduced in Rivi et al. (2016b) to measure galaxy ellipticities in the visibility domain for radio weak lensing surveys. In that paper we focused on the development and testing of the method for the simple case of individual galaxies located at the phase centre, and proposed to extend it to the realistic case of many sources in the field of view by extracting visibilities of each source with a faceting technique, taking into account the contamination from the other sources. In this second paper we present a detailed algorithm for source extraction in the visibility domain and show its effectiveness as a function of the source number density by running simulations of SKA1-MID observations in the band 950-1150 MHz and comparing original and measured values of galaxies' ellipticities. Shear measurements from a realistic population of 10^4 galaxies randomly located in a field of view of 1 deg^2 (i.e. the source density expected for the current radio weak lensing survey proposal with SKA1) are also performed. At SNR >= 10, the multiplicative bias is only a factor 1.5 worse than what found when analysing isolated sources, and is still comparable to the bias values reported for similar measurement methods at optical wavelengths. The additive bias is unchanged from the case of isolated sources, but is significantly larger than typically found in optical surveys. This bias depends on the shape of the Point Spread Function (PSF) and we suggest that a uv-plane weighting scheme to produce a more isotropic PSF could reduce and control additive bias.Calibration of weak-lensing shear in the Kilo-Degree Survey
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 467:2 (2017) 1627-1651
KiDS-450 + 2dFLenS: Cosmological parameter constraints from weak gravitational lensing tomography and overlapping redshift-space galaxy clustering
Monthly Notices of the Royal Astronomical Society Oxford University Press 474:4 (2017) 4894-4924